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spheric form in comparison with the megalospheric, a scarcity all
the more striking when it is borne in mind how far more numerous
are the zoospores produced by one megalospheric individual than
the members of a brood of megalospheres.



76 THE FORAMINIFERA

The analogy of other life -histories would lead us to suppose
that at some point in the cycle a sexual process, the conjugation,
with nuclear fusion, of two organisms, occurs, and the life-history
of Trichosphaerium sieboldi, Schn., which has lately been worked
out by Schaudinn (47), to whom so much of the recent advance
in our knowledge of the life -history of the Protozoa is due,
appears to afford a very appropriate parallel. This form is
not included in the Foraminifera, but is a somewhat aberrant
member of the allied group the Lobosa. The main features
of its life -history are, however, remarkably similar to those of
Polystomella.

The individuals are rounded multinucleated masses of proto-
plasm not contained in a definite shell, though surrounded by a
gelatinous envelope. They form a dimorphic series, the members
of which recur in a cycle of generations. In those of one genera-
tion, which may be called by Haeckel's term Amphionts, reproduc-
tion occurs by the simultaneous division of the protoplasm about
the nuclei to form spherical uninucleated masses, which emerge
and grow into the members of the other generation the Mononts.
These in their turn break up, after subdivision of their nuclei, into
zoospores. The zoospores are biflagellate organisms, and are all
alike.

While the zoospores from the same parent will not unite with
one another, those from different parents conjugate readily. In
this process, which has been carefully followed by Schaudinn, the
nuclei of the two gametes unite, their flagella drop off, and the
zygote so produced, absorbing fluid, undergoes a considerable in-
crease in size, so that in a few hours its diameter is more than
doubled. The zygote shortly afterwards secretes a gelatinous
envelope, and the characters of the full-grown individual of the
amphiont generation are gradually acquired. The multinucleate
condition results from successive mitotic divisions, beginning with
that of the nucleus of the zygote.

In Hyalopus dujardinii, which may be regarded as a member,
though an aberrant one, of the Foraminifera, Schaudinn (43) has
also observed the conjugation of zoospores, but in this case the
process occurred between members of the same brood.

If we assume that a similar conjugation of zoospores occurs in
Polystomella, the facts above alluded to are at once explained.

The fusion of two zoospores (4 p. in diameter), and the subse-
quent expansion of the zygote by the absorption of water before
the secretion of a shell, might well form a body of the size of the
microsphere (about 1 /*) ; the free locomotive stage prior to the
settling down of the microsphere, indicated by Schaudinn's
experiment, is supplied ; and the comparative rarity of the micro-
spheric form is explained on the supposition that, as in Tricho-



THE FORAMINIFERA 77

sphaerium, the meeting and conjugation of zoospores from different
parents is necessary for the production of a microsphere.

It is very desirable that the conclusion should be confirmed
by direct observation, but, meanwhile, it seems not premature to
admit that it is probable that the microsphere arises from the
conjugation of zoospores.

We may conclude, then, that the microspheric aad megalo-
spheric forms of the Foraminifera represent alternating or re-
curring generations in a life -cycle. While the megalospheric
generation arises asexually, either from a microspheric or a megalo-
spheric parent, it is probable that the microspheric generation
arises sexually i.e. by the conjugation of two similar zoospores.

Representatives of the two generations have been recognised
in species belonging to the following genera of Foraminifera :

ORDER l. Gromiidea (7). 1

( 2. Astrorhizidea. 2 )

( 3. Lituolidea.)

4. Miliolidea.

Family MILIOLINIDAE. Cornuspira (24, 1898, p. 612); Spiro-
loculina (57, p. 201); Biloculina (27, p. 863); Sigmoilina (Planispirina,
pars), Schl. (53, p. 106) ; Triloculina and Quinqueloculina (27, pp. 863
and 1598); Massilina (57, p. 218); Adelosina (52, p. 91); Idalina
and Periloculina (28) ; Lacazina (27).

Family HAUERINIDAE. Planispirina, Seg. (56, p. 194).

Family PENEROPLIDIDAE. Peneroplis and Orbiculina (this article),
Orbitolites (4, p. 693, and this article) ; Meandropsina (59).

Family ALVEOLINIDAE. Alveolina (51, p. 526).

ORDER 5. Textularidea.
Family TEXTULARINAE. Textularia and Spiroplecta (this article).

(ORDER 6. Chilostomellidea.)
7. Lagenidae.

Family NODOSARIIDAE. Nodosaria and Dentalina (51, p. 626);
Frondicularia (15, p. 480) ; Cristellaria (?) (5, p. 45).

Family POLTMORPHINIDAE. Siphogenerina (Sagrina) (50, p. 21).

(ORDER 8. Globigerinidea.)
9. Rotalidea.

Family ROTALIDAE. Rotalia (51, p. 526, and 20, p. 436);
Truncatulina and Calcarina (20, pp. 436 and 437).
Family TINOPORIDAE. Polytrema (23).

1 The cases of Hyalopus and Mikrogromia are considered below. .
3 In the orders included in brackets I have not succeeded in finding a record of
the existence of dimorphism.



78 THE FORAM1NIFERA



ORDER 10. Nummulitidea.

Family FUSULTOIDAE. Fusulina (58, p. 1).

Family POLYSTOMELLIDAE. Polystomella (20, p. 415).

Family NUMMULITIDAE. Operculina (this article); Amphistegina
(51, p. 526) ; Nummulites and Assilina (26, p. 300) ; Heterostegina (this
article); Cycloclypeus (10, p. 21, and this article); Orbitoides (31, p.
258, and 61, p. 463) ; Miogypsina (60, p. 328).

Thus the phenomenon of Dimorphism, the occurrence of mem-
bers of a species under two forms the megalospheric and micro-
spheric is widely spread among the orders of the Foraminifera,
and where it is found it affords clear evidence of alternating or
recurring generations in the life-history of the species exhibiting it.



REVIEW OF THE STRUCTURE AND LIFE-HISTORY DISPLAYED
IN THE ORDERS OF THE FORAMINIFERA.

As the attention of the many workers who are occupied with
this group is turned to the subject, the list of dimorphic forms
will, no doubt, be greatly extended ; but there are indications in
the descriptions already published of phases in the life-history of
some forms, especially in that borderland occupied by the simpler
Foraminifera, which depart in a greater or less degree from those
described in Polystomella and Orbitolites ; and we may now take a
survey of the features of life -history which have been described
in the different groups, and of the more interesting modifications
in the form of the test, which, as we have seen, is found to be
more or less dependent on the phase of the life -history of the
organism which secretes it.

In chambered tests, in which the walls of the first formed
chamber remain unaltered throughout growth, evidence of the
mode of origin of the individual, whether as a megalosphere or a
microsphere, is furnished by the structure of the test. But in the
great majority of the Gromiidea and Astrorhizidea, the tests expand
to accommodate the increase by growth (cp. p. 54), and all in-
dications of the size of the test when it was first secreted are
obliterated. Hence we are deprived in them of part of the evidence
on the course of the life-history which we have in other groups,
and we must rely on the characters furnished by the soft parts
of preserved specimens, or on direct observation of the living
animals.

From the evidence which we have, however, it is not clear
that the course of the life-history of some members of these orders
is the same as that of the dimorphic Foraminifera above described.



THE FORAMINIFERA



79



ORDER Gromiidea.

In Euglypha (Fig. 3) multiplication, by division into two,
occurs as follows. 1 The specimen which is about to divide
secretes fresh shell plates, which are at first dispersed in the
protoplasm about the nucleus. The pseudopodia are with-
drawn, and the protoplasm is extruded beyond the mouth of the
test in a rounded mass. This grows until it assumes a size
equal to that of the test from which it protrudes, and the
newly-formed plates are disposed on the surface to form a new
test. The nucleus divides by karyokinesis, half going to each
end of the mass, and division of the protoplasm follows, one part
remaining in the old shell and the other in the new one.




FIG. 14.

Colony of Mikrogromia sodalis in the diffused condition, a, an individual in process of
multiplication by transverse fission, c.v, contractile vacuole. Two of the members of the
colony are seen to be undergoing the same process.

Blochmann (2) has described a process in which, after the
division of the nucleus, the protoplasm was withdrawn from the
newly formed shell, and this, together with the daughter nucleus
remaining in it, was cast off. It is suggested that this may be
comparable with the extrusion of parts of the nucleus observed in
some other Protozoa and in polar-body formation. But in view
of the fact that the new shell was cast off, as well as the daughter
nucleus, this interpretation appears, to say the least, forced.

A temporary fusion of the protoplasm of two or more indi-
viduals, apparently without fusion of nuclei (plastogamy), was
observed by Blochmann, and in one instance a new individual was
apparently formed by the conjugation of two. In this case it

1 The process was first described by Gruber (16), and followed out in detail by
Schewiakoff (48).



8o



THE FORAMINIFERA



was supposed that the nuclei had united (karyogamy) as the new
individual was uninucleate.

Encystment also occurs in Euglypha, but what the subsequent
stage may be is unknown.

Mikrogromia socialis, first described by Archer, 1 and afterwards
more fully by R. Hertwig (18), is a fresh-water form, occurring in
colonies, the members of which are united by their pseudopodia.
The colonies are sometimes globular and compact (Cystophrys
sta^c;, sometimes diffused (Fig. 14), and in the latter condition
present an interesting resemblance to a brood of young megalo-
spheric individuals of Polystomella in a stage of dispersal
(Fig. 10, d).

The growth of the colony results from the partial longi-
tudinal fission of the members into two (or three), one (or two) of

the products of fission escaping,
secreting a new test, and taking its
place in the colony. Hertwig also
observed the production of young
individuals, arising by transverse
fission (Fig. 1 4, a). Of the two bodies
so formed one remains in the test,
continuing the vegetative phase of
the parent, the other becomes free,
and, in some cases, swims away as
a biflagellate organism. In other
cases, however, the flagella were not
observed, being replaced by pseudo-
podia, resembling those of Actino-
phrys. The further history of the
young thus produced was not
followed. Assuming this to be a
normal phase of development of
Mikrogromia, it appears to be with-
out a parallel in the life-history of
Polystomella.

Hyalopus dujardinii, Schaudinn
( = Gromia dujardinii, M. Schultze) is
a marine form distinguished by the
hyaline and nongranular character of
its pseudopodia, and by the absence
of anastomoses between their branches.
The main body of the protoplasm is
covered by a chitinous envelope, and contains large brown
rounded granules and many nuclei. In the condition in which it

1 Provisionally as two species, Cystophrys haeckdiana and Oromia tocialis
Archer (1).




Fio. 15.

Hyalopus (Gromia) dujardinii.
(After M. Schultze.)



X 40.



THE FORAMINIFERA



81




FIG. 16.

5, Shepheardella taeniformis, Siddall, x about 15. (After Siddall, Q.J.M.S vol. xx.) The
nucleus is seen nearly opposite 5. 11, Amphitrema wrightianum, Archer, x^about 210. (After
Archer, Q,J.M.S., N.8. vol. ix. 1869.)



82 THE FORAMIN1FERA

was described by M. Schultze (64, p. 55), the shape is oval, and
there is a single orifice (Fig. 15), but Schaudinn finds (43) that
when living amongst the stems of algae, it loses its oval shape
and assumes a branching form, new mouths being developed at
the ends of the branches. Such branched forms may attain a
length of 5 mm.

Two modes of reproduction were observed. One is by a
process of fission, the body slowly dividing into two or three
parts, sometimes of unequal sizes ; the other is by the formation
of zoospores. In the latter process the pseud opodia are retracted
and the whole protoplasm divides up into oval or pear-shaped
bodies, 5-8 /i in diameter, containing a nucleus 3-6 //. in diameter,
a vacuole, and a conspicuous granule. They swim by means of
a single tiagellum 30-38 /x in length.

The zoospores conjugate in pairs, but in this case the conju-
gation is, according to Schaudinn, between members of the same
brood. The further history of the zygote could not be followed.

The formation of the zoospores of Hyalopiis is evidently com-
parable on the one hand with the reproduction of Trichosphaerium
which gives rise to the " amphiont " generation, and on the other
hand with the reproduction of the megalospheric form of Polysto-
mella.

A similar mode of reproduction to the slow process of fission
of Hyalopus has been seen in Lieberkiihnia and Lecythium, the
division of the protoplasm involving that of the envelope. Whether
this is to be compared with the production of the brood of
melagospheres by the multiple fission of the microspheric parent,
or to the similar slow fission which occurs in Trichosphaerium in
addition to the multiple fission of the "amphiont" parent, it
appears to be at present impossible to decide. Many of the
Gromiidea have a single orifice to the test, as in Gromia and
Eugbjpha (Figs. 1 and 3). Shepheardella and Amphitrema have two
orifices, situated at either end of a median axis (Fig. 16, 5 and 11).

ORDER Astrorhizidea.

In Saccammina, and some other members of the Astrorhizidea
in which growth is accompanied (as explained above, p. 54) by
expansion of the test, no evidence on the phase of life-history
represented, is furnished by its structure. But in other genera,
such, for example, as Hi/perammina, in which the tests grow not
by expansion, but by addition, a large globular chamber is some-
times found at the commencement (Figs. 17, rf, and 18). Such
forms may well represent a megalospheric generation. There
is, however, no evidence at present of the microspheric forms
corresponding to them.

Rhumbler has made a careful investigation (33) of the nuclear



THE FORAM1NIFERA



characters of Saccammina sphaerica (Fig. 17, b). He found that
among the 286 specimens which he examined, a single nucleus
was present in all but one
(which had two nuclei, and
was regarded as abnormal),
and the phases presented by
the nuclei fell into a con-
tinuous series. They corre-
spond with those of the nucleus
of the megalospheric form of
Polystomella. The nucleus in-
creases in size with the growth
of the organism, and the
nucleoli ("binnen korper"), at
first large and few, increase
in number and diminish in
size. Finally (PI. 23, Fig. 67)
the nuclear membrane breaks,
and linin threads containing
chromatin grains are dispersed
in the protoplasm. From these






Fio.



a, Astrorhiza limicola, Sandahl., x 6. I, Sacaimmiiia sphaerioa, M. Sar*, x!2. c, Piluli)ia
jefreysii, Carpr., x 12. d, Hyperammina subnodota, Br., x 7. In a, b, and d the test lias been
laid open. (From Brady, "Challenger" Report.)

later nuclear phases it appeared that some process of reproduction
was imminent, but none was observed. The formation of zoospores
by the Foraminifera was at that time unrecognised, and Rhumbler



THE FORAMINIFERA



was surprised at finding no indication, notwithstanding the
abundant material at his command, of the formation of a brood of
young resembling the parent. On the analogy of the life-history
of Polystomella, the absence of such indications appears in no way
remarkable, for such a nuclear history is associated, as we have
seen, with the production of zoospores.

The only difficulty in applying this analogy arises from the
fact that no indications were found of a form of Saccammina with

a different nuclear history,
corresponding with that of
the microspheric generation of
Polystomdla.

It is, of course, possible
that the microspheric form,
although occurring in nature,
did not happen to be repre-
sented among the specimens
examined; but however this
may be, it is clear that we are
not at liberty to assume the
existence of a microspheric
form in Saccammina. Hence,
in the absence of other evi-
dence bearing on the point,
the Astrorhizidea cannot at
present be admitted into the
list of dimorphic Foramini-
fera.

In Haliphysema tumano-
wiczii (Fig. 19) Lankester (19)
described numbers of "egg-
like " bodies, varying in diam-
eter from T-gVfr to -5^5- inch,
scattered through the proto-




Fio. 18.



H yperammina arborescent, Norm, o, two speci-
mens growing attached to a stone, x 20 ; b, initial
chamber of another specimen. (After Brady.)



plasm. They appeared to be
nucleated, and, in some cases,
in process of division. It was

surmised that they might be concerned in reproduction. Further
information on the nature of these bodies would be very accept-
able, but the possibility appears not to fcave been excluded that
they are symbiotic or parasitic organisms similar to those which
abound in the protoplasm of Orbitolites complanata.



THE FORAMINIFERA



ORDER Lituolidea.

This order consists of arenaceous forms which are "isomorphic"
with genera belonging to several of the other orders; and by
many authors the order is broken up, and its genera associated




10



Fio. 19.

Haliphysema tumanvwlczii. 10,
part of the protoplasm stained to
show the nuclei, ; 11, living speci-
men with expanded pseudopodia.
(From Lankester, Art. Protozoa,
Encycl. Britannica, Fig. x.)



with the calcareous forms which they resemble. In some cases
(e.g. Cornuspira, Nodosaria, Eotalia) the latter are, as will appear
below, dimorphic, so that we should expect their " isomorphs " to
be so likewise ; but though this is very probably the case, I am
aware of no direct evidence on the matter.

A process of reproduction is recorded by Schaudinn (42) in
Ammodiscus gordialis, P. and J. The protoplasm divides within
the parent test into some 50-80 young, which become invested



86



THE FORAMINIFERA



with a chitinous envelope, together with siliceous particles pre-
viously taken into the protoplasm.

ORDER Miliolidea.

On coming to the Miliolidea we have a large body of evidence
on dimorphism, thanks in great measure to the careful investiga-
tions of Schlumberger, by whom, either alone or in conjunction
with Munier-Chalmas, the foundations of our knowledge on the
dimorphism of the tests of Foraminifera have been laid. The tests
will first be described, the nuclear characters and such details of
the life-history as are to hand being given at the end.

Family Miliolinidae. Before considering the phenomena of
dimorphism in this family, it is necessary to describe the character-
istic structure of the test in certain forms.





FlO. 20.

Comuspira involvens, Reuss. a, the megalospheric
form, x 90. b, the microspheric form, x 60. (From
Brady, Parker, and Jones, Tran* Zool. Soc. vol. xii. PI.
40, Figs. 1 and 2.)




FIG. 21.

Spiroloculina limtxita, d'Orb.,
x 80. (After Brady.)



The simplest type is met with in Cornuspira.

The whole of the test except the central chamber (which pre-
sents a well-marked difference in size in the two forms, Fig. 20)
consists of a continuous tube, gradually increasing in diameter as
it is followed away from the centre, but without any constrictions
dividing it into separate chambers. In both forms it is disposed
in a closely-wound spiral lying in one plane, so that a section in
this plane would divide the test symmetrically.

In the genus Spiroloculina the arrangement is somewhat similar,
but here the tube is divided into distinct chambers, each of which
ends in a contracted mouth with an everted lip. The chambers
increase successively in length, and are so disposed that each
occupies half a turn of the spiral. It results from this arrange-
ment that the mouths of the chambers are directed alternately in
opposite directions, and each chamber is applied to that which is
next but one before it in the series. A straight line, which passes



THE FORAMINIFERA



through the central chamber and the mouths of all the chambers
which succeed it, has been called the axis of construction. The
spiral formed by the series of chambers is not quite regular, as is
the case in Cornuspira ; for while each chamber is gently curved,
there is a sharp bend where one chamber communicates with
another. Hence the test is elongated in the axis of construction.
In Spiroloculina the chambers are disposed in one plane, and the
width of each is only slightly greater than that of its predecessor,
so that all the chambers are exposed on the two flat faces of the
test (Fig. 21).

In all but the earlier chambers of the microspheric forms the
arrangement characteristic of the genus Biloculina is essentially
similar, but there is a marked difference in the shape and appear"-
ance of the test owing to the great width of the chambers. Each




Fio. 22.

a, Biloculina dcpressa, rt'Orb., x 40. b,
Triloeulina tricarinata, d'Orb., x 50. (After
Brady, 3.)

is so wide that its margins are in contact with those of its prede-
cessor, and overlap them at the sides (Figs. 22, a, and 24). It results
from this arrangement that the two last chambers enclose those
previously formed, and they alone appear in the contour of the
test. As in the preceding genus a median longitudinal section
through the last chamber divides the whole series of chambers
into symmetrical halves. As will appear later, the microspheric
form of Biloculina departs considerably from this arrangement.

In Triloculina and Quinqueloculina 1 the chambers are likewise
disposed about an axis of construction, and their mouths open
alternately in opposite directions, but the median plane of any
chamber is not that of its predecessor, but directed at a definite
angle to it. It is as though in a Biloculina test, while the plane
in which the new chambers are formed remains constant, the

1 These genera are now usually included in the genus MUiolina, though Schlum-
berger is inclined to retain the old generic distinctions.



88



THE FORAMINIFERA




Fio. 23.



Quinqutlocnlina $eminulum, Linn, a-c, views of teat ; a, b, from the Bides ; c, from apertural
nd. A, section of megalospheric, B, of microspheric form. A and B from Schlumberger (57).
It will be noticed that A and B represent a less flattened form of test than that seen in a-c.



THE FORAMINIFERA 89

part of the test already formed were to rotate on its axis of con-
struction through a definite angle in the interval between the
formation of one chamber and the addition of its successor. In
the genus Triloculina the rotation is through (approximately) one-
third of the circumference, in Quinqueloculina through two-fifths,
and the chambers are disposed in three and five radii respectively.

In these genera the width of the chambers is, moreover, less
than in Biloculina ; and in Triloculina three, in Quinqueloculina five
chambers are exposed, at any given stage of growth on the contour
of the test.

We may now turn to the phenomena of dimorphism as pre-
sented by members of this family.

In representatives of all the genera included in the list on
p. 77, a well-marked difference has been shown to exist in the
size of the central chamber in the two forms of the species. Thus
in Biloculina depressa the diameter of the megalosphere (M) x has
been found to vary from 200 to 400 /*, and that of the micro-
sphere (m) 1 from 18 to 25 p (Fig. 24).

In B. ringens the contrast is not so great (M = 54 /*, m = 20 /A).
In Triloculina M = 204 & m= 18 p. In Sigmoilina M- 96-150 ft,
m- 27-3 6 i*. In Adelosina M= 90-330 /*, m= 18 p. In Idalina
M- 180-440 fly m = 12 p. In Massilina a well-marked difference
is said to be present, though the actual dimensions are not
recorded.

Turning to the plan of growth, in Cornuspira and Quinquelocu-
lina the tests are uniform, i.e. they are arranged on the same
plan throughout, from the part which immediately succeeds the
central chamber to the end of the test ; and this is the case in
both forms of the species. Massilina has biformed tests in both
megalospheric and microspheric forms, the earlier chambers being
arranged on the quinqueloctiline plan, and the later on the spiro-



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