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occipitomaculata taken in the hardwoods near North Fishtail Bay on
Douglas Lake contained three red-backed salamanders, and the fact that
the food of the red-bellied snake may include tlie grass snake has been
mentioned previously.

The box turtle and the skink represented as they were by but a single
specimen each in the collections of four summers are too rare to be con-
sidered in this connection.

Series 4- Habitat of both larvae and adult strictly aquatic. The mud
puppy, Necturus maculosus is the only species in the fauna considered
which comes imder this head. This species is not common in the Douglas
Lake region at present.

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The most obvious changes in tlie liabitats of the Douglas Lake region
have been those attending . the removal of large areas of virgin timber
by cuttings fire, or both. These changes in the vegetation of the wood-
land habitats have had a direct effect upon the fauna of the areas so
altered. Where the land has been completely cleared a new forest of
aspens has appeared and in the partly cut-over forest areas, the disturbed
hardwoods, underbrush which is so conspicuously absent in the virgin
timber, berry vines and second growth timber, have come up. These
changes affect the upland and forest forms more than the semi-aquatic
types of amphibians and reptiles. The fauna from the surrounding
habitats overflows to some extent into the recently burned-over areas
and in the growths of fireweed, Epilobium angustifolium, which are
common in burned-over areas during the first two or three years after the
fire. Woodland species, Bufo americanus and Rana cantabrigensU were
frequently found near the undisturbed timber. In the underbrush and
second growth timber which follow the fireweed, the grass snake, Liopel-
tis vemalis seemed to be increasing in abundance. After the burned over
timber had fallen and begun to rot Plethodon eryihronotus again appeared
in the burned-over areas if there were sufficient vegetation to insure a
moist habitat. Rana pipiens and Thamnophis sirtalis were often seen in
rather open burned-over country, but always near some other more favor-
able habitat, and as has been noted in another section, these two species
were more widely distributed than any other species of this fauna.

The semi-aquatic species seem to have suffered little in the region.
Forest fires and the clearing of timber have disturbed the lakes, streams
and especially the waterlily associations which are so vital to the success
of the primary amphibian species, little if at all. Bogs have been burned
over frequently, although the central body of open water usually remains
after the bog timber has been destroyed.

A noticeable exception to the undisturbed condition of the aquatic
habitats of the region may be cited as showing how important slight
changes may be in determining the local distribution of species. A large
number of g'artersnakes were collected near a certain beach pool on Sedge
Point, Douglas Lake, during the summer of 1915 for use at the Biological
Station. Apparently correlated with this- destruction of a dependent
species of snake during the previous year, was a noticeable increase in
the number of young frogs in the same habitat during the summer of
1916. Although young fi'ogs, one of the regular items in the food of
these gartersnakes in the Douglas Lake region were abundant, few gar-
tersnakes were taken in this habitat in 1916.

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1906. Dickerson, Mary C. The Frog Book. New York.

1907. Ditmars, R. I.. The Reptile Book. New York.

1915. Evans, A. T. A Collection of Ampliibians and Reptiles from
Gogebic County, Michigan, Proc. U. S. N. M., Vol. 49, pp. 351-854.

1915. Gaige, Helen T. The Ampliibians and Reptiles collected by
the Bryant Walker Expedition to Scljoolcraft County, Michigan, Occas.
Papers, Mus. Zool. University of Mich., No. 17, pp. 1-5.

1892. Hay, O. P. The Batrachians and Reptiles of Indiana. Rept.
Ind. Dept of Geology and Nat. Resources, Vol. XVII, (1891), pp.

1911a. Ruthven, A. G. Amphibians and Reptiles in a biological sur-
vey of the sand dune region on the south shore of Saginaw Bay, Michi-
gan, Geol. and Biol. Surv. Mich. Pub. 4, Biol. Ser. 2, pp. 257-272.

1911b. Ruthven, A. G. Notes on Michigan Reptiles and Amphi-
bians, III, Thirteenth Ann. Rept. Mich. Acad', of Sci., pp. 114-115.

1912. Ruthven, A. G., Thompson, Crystal and Thompson, Helen,
Herpetology of Michigan, Geol. and Biol. Surv. Mich. Pub. 10, Biol Ser.
3, pp. 18-815.

1906. Surface, H. A. The Serpents of Pennsylvania, Zool. Bull.
Penn. Dept. of Agri. IV, pp. 118-202.

1912. Thompson, Crystal and Thompson, Helen. Results of the
Shiras Expedition to Whitefish Point, Michigan, Amphibians and Rep-
tiles, Fourteenth Ann. Rept. Mich. Acad, of Sci., pp. 216-217.

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The larvae of many amphibia possess epidermal sense organs similar
to the lateral line organs of fishes. This report deab briefly with the
structure and distribution of the lateral line organs of the tadpoles of
Rana clatnitans, from which species they have not heretofore been re-
ported. The species was determined by illustrations and descriptions in
Wright's "North American Anura.*'

The tadpole possesses several rows of lateral line organs, which are
located chiefly on the dorsal and lateral surfaces, although a few extend
onto the anterior ventral surface. The distribution conforms to a definite
system, with minor individual variations. These rows are made up of a
series of light colored dots, each dot representing one or more of the
sense organs. While the sense organs usually occur singly or in pairs,
six or eight are sometimes found side by side. Kingsbury believes
that such groups of sense organs are produced by fission from a single
original sensory structure.



Figure 1. Tadpoles of Rana clamitans, showing distribution of sense organs.
Length, 4 cm.

Distribution. Beginning from a point slightly behind the eye, two
diverging rows extend backwards along the body and the tail. The inner

iftth Mich. Acad. Sd. Rept.. 1917.

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one runs along the upper iialf of the fin for about two-thirds of its
length, nearly midway between the border of the fin and the myotomes.
The second extends back, following the centre of the myotome region,
nearly to the tip of the tail. A pair of short rows are located dorso-
laterally on either side of the head. They run backward, one row of
each pair passing on either side of the nares and the eye. Behind the
eye, the organs are rather irregularly arranged, although one or more
short definite rows may occur. The anterior lateral surface bears other
rows of sense organs, as shown in the diagram, (Fig. 1.). The distribu-
tion of the lateral lines is practically identical with that in Rana
catesbeana, as described by Kingsbury.

Structure, As regards structure, these sense organs, when seen in
vertical section under the microscope, closely resemble taste buds. They
are composed of a cluster of somewhat conical cells radiating from a
more or less pronounced pit or crater in the outer surface of the skin.
The cluster usually extends the full depth of the epidermis. Kingsbury
recognizes two kinds of cells, a few shorter inner cells, surrounded

Figure 2. ( titans, showing

structure of a lateral line organ.

by several longer, slenderer ones. Fig. 2 shows two nuclei separated
from the others, and lying nearer the surface, which probably represent
the nuclei of the inner and shorter cells. The nuclei of the cells com-
posing the sense organs are situated at the inner end of the cells, and the
cytoplasm is relatively clear. The structures are, in general, similar to
those figured by Kingsbury for the larvae of Amblystoma, and several
other Urodeles, except that in the case of Rana clamitans, the cells com-
prising the sense organ are shorter and less numerous.


Dickerson, Mary E. 1907. The Frog Book, p. (5.

Kingsbury, B; F. 1895. The Lateral line system of Sense Organs in
some American Amphibia, and Comparison with Dipnoans. Proceedings
of the American Microsco])ical Society, Vol. 17, pp. 115-151'.

Wright, A. H. 191 K North American Anura.

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Since the discovery and description of the genus by Ehrenberg in 1 880^
Arcella lias been a favorite subject for microscopic investigations. It
is^ without a doubt^ our most common fresh water shell-bearing rhizopod^
and may be found in a large proportion of cultures taken from ponds
and streams. Combining amueboid simplicity of organization with a
complicated system of reproduction, and added to this a shell rivalling
those of .the Foraminifera, it is scant wonder that for the past half
century the literature on the subject has continued to accumulate. Many
and diverse conclusions have been reached by separate workers. It is
in an attempt to embody the most conservative of these in a connected
account, together with personal observations, that this article is written.


In appearance, Arcella is distinctive. In spite of marked variations in
form within the genus, it is not liable to confusion with any other com-
mon Protozoon. The comparison that inevitably presents itself on seeing
the organism for the first time, is that it looks like a little doughnut. The
yellow or brown color, circular shape, and small central opening, favor
the simile.

From the side, however, the shell is seen to be campanulate in shape,
broadest at the bottom, and wider than high. Across the bottom of the
inverted bowl extends a continuation of the shell, covering the base
except for a round central opening, one-fourth to one-third the diameter
of the shell. The surface of the dome is generally smoothly convex,
but may be pitted or faceted. The color varies from faintest yellow
through brown, almost to black. Average dimensions are .1mm wide,
.05mm high, with a mouth opening of .03inm. In all cases except very
young individuals, a minute configuration or cancellation of the shell is
visible. Unlike the related Difflugias, A rcella never has sand or other
foreign particles incorporated in the shell.

Within the shell can be seen a mass of clear protoplasm of irregular
outline, usually filling most of the shell cavity. Two nuclei are commonly
visible, but there may be only one or many. Contractile vacuoles, gas
vacuoles and food balls are features usually distinguishable without

lOtb Mich. Acad. Sci. Rept., I017.

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special preparation. From the opening of the shell extend long, slender
pseudopodia. The protoplasm is attached at base and dome in a wavy


Physiologically, Arcella is quite amoeboid, within the restrictions im-
posed by the shell and other factors. It progresses by the same pseado-
podial action, and is similar in food relations. Due to the mechanical
impediment of the shell, it cannot advance witli the effective rolling
motion of the larger amoebas, but must laboriously extend its pseudopo-
dia, contract its protoplasm, and drag its shell forward. It creeps about
the leaves of water plants and on the bottom debris of shallow, sheltered
water. In a culture jar, its method of locomotion is evident, but progress
is exceedingly slow.

Generally several long, clear pseudopodia are extended to one side.
They are clear and transparent except for ingested food particles, and are
normally simple, but may be briinched. Now and then an individual is
seen to extend a long slender pseudopod and wave it slowly back and
forth. Some authors have interpreted this as ''feeling for food," but to
Calkins ('10), it suggests the origin of flagellar structures.

In its food and feeding habits, the present genus is not markedly differ-
ent from the better described Amoeba, The pseudopodia are so long and
slender that it is confined for food to the ooze of decaying vegetation,
and to certain algae. Although a considerable part of the body pro-
toplasm may be extruded from the shell, the latter is an effective hin-
drance to engulfing large and vigorous Infusorians.

If a food particle is encountered small enough to be manipulated by
the thread-like pseudopodia, it is ingested and passes slowly to the body
mass, where digestion is completed. If it is too large to be disposed of
in this way, other pseudopodia may be projected and the whole body
drawn up to a point over the particle. Within the body the nutriment
is absorbed and the indigestible particles egested. This naturally occurs*
at the mouth of the shell, so that there is a localization of egestion slightly
in advance of the amoeba. Contractile vacuoles are numerous and active.
There is no evidence that any particular selection of food occurs. There
is, however, a degree of discrimination indicated by the fact that sand
particles and other indigestible materials are not ingested to any great

In cultures rich with algae, the Arcellas creep about and become filled
with the smaller organisms in normal fashion. An astonishing phenom-
enon, however, is the ingestion of a filamentous alga twenty or thirty
times as long as the diameter of the shell. How it is possible for the
animal to coil the long strand within its shell is a problem, but the fact

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remains that it is often so found. After watching the operation a number
of times^ it is my conclusion that the phenomenon is due merely to the
shape of the shell and filament and the nature of the engulfing force.
An end of the strand is encountered and ingested. As it strikes the
dome of the shell, it bends to one side or the other^ and continued exertion
results in the coiling of the filament as the most conservative mechanical
mode of disposition.

As a matter of fact, similar cases are observed in the inorganic world.
Calkins ('10) states that a drop of chloroform will draw in a thread of
shellac in the same way, as will also egg albumen with gum arable. The
implication is that many of the vital processes of lower forms, like in-
gestion and excretion, are not different in kind from physical processes
occurring quite outside the organic realm.


The possibility of anotlier mode of locomotion than that of pseudopo-
dial progression has received considerable attention. Long since, at
least by the time of Engelman ('69), gas bubbles were observed in
Arcella, which grew in size and then subsided, apparently without refer-
ence to external conditions. Since that time these have been considered
as hydrostatic organs, capable of raising or lowering the body in thr
water. Whether or not this function is purely a myth is not yet clear.

The gas bubbles appear in all places in the body, are irregular in shape,
and have no constant relation to the nucleus and contractile vacuoles.
Khainsky ('10) remarks that the change in volume usuaUy occurs in
all the bubbles of one individual at the same time. This has its excep-
tions, as not all the bubbles change size at the same rate.

The nature of the gas contained has been variously regarded as oxygen,
carbon' dioxide, and atmospheric air. Dr. Khainsky (op. cit.), who seems
to be the only recent worker on the subject, declares the gas to be neither
oxygen, carbon dioxide nor sulphur dioxide, as indicated by appropriate
tests. Furthermore he states that they do not appear in cultures where
there are no algae, that they grow at night and diminish by day, and
are never present in young individuals. Finally he surmises that the
bubbles gain access to the shell by the animal climbing to the surface
film and elevating the shell into the atmosphere by pseudopodial action.
His conclusion is equally remarkable: "The gas bubbles play no physio-
logical role with Arcella, and for the organism itself are only harmful.

The Arcellas which contain gas vacuoles always die." "In

den FftUen wo die Arcellen mit Blasen an irgendeinem Gegenstand
anhaften, pressen sie die Gasblasen durch die Schale heraus," assuming
the shell to be porous.

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My own incomplete observations, covering some montlis with many
thriving cultures, give no direct evidence of hydrostatic activities,
although the bubbles themselves have been numerous. I have never
found Arcellas in a location where they might not normally have arrived
by other means.

My theory of the origin of the gas vacuoles is in line with Khainsky
elsewhere. The newly formed Arcella has a shell very soft and flexible
so that it yields to the contractions of the protoplasm. As it becomes
hardened, it no longer gives with the same ease. The contracting pro-
toplasm pulls away from it, forming a slight vacuum, into which the
dissolved gas of the culture evolves. Under pressure again, this redis-
solves, thus accounting by a simple physical law for the irregularity of
the appearance and disappearance of the vacuoles. Such a process would
alter the specific gravity of the organism, but whether it would be sufficient
to accomplish flotation is not certain.


General Features. On the basis of shell morphology, the genus Arcella
is customarily divided into half ^ a dozen species. The type species,
//. vulgaris £hgb. has been mentioned. A discoides Ehgb. is lower and
broader, generally shield-shape. In A. mitrata Ixidy the shell is mitri-
form, higher than wide, and widest at or near the middle, generally with
the sides of the dome divided into regular facets. A, dentata Ehgb. is
characterized by pronounced dentate processes around the base.

In spite of these rather conspicuous differences, the forma intergrade
completely, so that it is impossible to be certain of the specific rating of
many individuals. The statement is made (Claparede and Lachmann
and others) that individuals of one form may produce others totally dis-
similar, so that the specific nomenclature is valid for convenience of
description only. Occasionally I have found an abnormal shell, but such
are quite exceptional. A noteworthy case was one with a double mouth
opening. Pseudopodia proceeded from one or the other without discrimi-
nation. Other abnormalities apparently have resulted from injury, with
incomplete regeneration of the part lost.

Minute Anatomy, The details of the finer structure of the shell have
been the subject of much discussion. A regular cancellation of the sur-
face is apparent, even with moderate magnification, but the nature of
the construction is not so clear. The stock description has been that of
Leidy ('79), who states that the test **is composed of a more or less
translucent or transparent chitinoid membrane, with a minutely cancel-
lated hexagonal structure.'** From the text and figures, it is plain that
he considers the shell to be composed of closed hexagonal chambers like

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those in a honeycomb. This idea may be traced to Hertwig and Lesser
('74), who, after considering and rejecting former views, declare posi-
tively: "Ihrer feineren Struktur nacli besteht die Schale aus zwei Plat-
ten, einer ilusseren und einer inneren, welche einander parallel gelagert
sind, und durch ein bienenwabenartiges hexagonale Figuren bildendes
Fachwerk vereint werden."

The same authors treated the shell with sodium carbonate and acetic
acid, whereby bubbles were formed in the cancelli, showing them to be
hollow. The fact that the chambers were closed above and below has
never been questioned until recently. Cushman and Benedict (*06) are
of the opinion that there is only one membrane, the inferior one, so that
the cancelli are open above. They say that by exposing the shell to the
air, bubbles collect in the chambers without further treatment. Excellent
photomicrographs showing this result are included in the work, and they
state that in cross sections no superior membrane appears. On the con-
trary, however, the later careful work of Khainsky ('10) indicates both
membranes in sectioned preparations. It is barely possible that both
are right. If the original cancelli were constructed with delicate end
plates, it is conceivable that these might later be ruptured or dissolved.

Aside from this point, the fine anatomy of the shell seems to be com-
plicated beyond the conception of the earlier writers. Cushmann and
■ Benedict ('06) give photomicrographs which show clearly that the struc-
ture is not the simple hexagonal one usually figured. In the typical
hexagonal structure, all six sides are in contact with similar sides of
other hexagons, while in the shell pattern of Arcella, the sides of the
hexagons are never in contact with each other, but with smaller triangular
figures. The scheme may be reproduced by drawing three sets of parallel
lines at an angle of sixty degrees with each other.

Origin and Formation. The manner of construction of this compli-
cated shell is worthy of note. For a long time, it has been a common
observation that new Arcellas were formed by fission and constructed
a new shell from intrinsic material. This rudiment of the shell is so
flexible and transparent that it has generally been held to be structureless.
Khainsky, however, discusses certain intra vitam stains which render the
structure visible during formation. He states that after the emergence
of the protoplasm from the cavity of the maternal shell, a clear delicate
membrane is secreted around the projecting plasma. This under sufficient
magnification exhibits an irregular foam structure, with larger and
smaller alveoli promiscuously intermingled. At this time, these are plas-
tic and flexible. As growth proceeds, due to side pressure they become
higher and assume the typical hexagonal shape, with the smaller alveoli
filling the interstices between the larger. . At this time the shell of the

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new Arcella is closely united to the ectoplasm of the maternal sarcode.
Soon the shell begins to take on its characteristic shape^ and fission of
the protoplasm results in two daughter cells, each with typical amoeboid
activities. The young cell is distinguished by a lighter color, which
gradually deepens with age.

Chemical and Physical Characteristics. As has been anticipated, the
shell of Arcella is chitinoid in composition, resembling the protective
exoskeleton of the Arthropods. It is insoluble in all ordinary acids and
alkalies, a feature of immense significance to the organism. In some ex-
periments of my own, digestion in water at room temperatnre for half a
year failed to produce any appreciable effect, while it reduced insect
structures entirely, with the exception of the elytra and mandibles.

The brownish color is evidently due to iron salts deposited in the shell
substance. Awerinzew's "Arbeit nach enthalten die Arcellash&len Eisen,"
as well as Khainsky's statements, support this view. Further support
is derived from the fact that the animals thrive best in water rich in
minerals, and do not propagate in the acid water of bogs where Actino-
phrys is found. As to the general chemistry of the shell, Khainsky sug-
gests that in the young shell an oxyaminoacid is present, which is altered
with age by the substitution of iron.


The reproductive processes in Arcella are remarkably varied and com-
plex for an animal of so simple organization and especially one of free-
living habit. All the elementary types of reproduction known in the
Protozoa have been described for this single genus.

Fission. The simplest manner of reproduction is that in which n
mature animal divides into two daughter cells, and it is this type of propa-
gation that was first described in the genus. As physiological maturity is
reached, the protoplasm of the maternal cell proceeds to the mouth of
the shell, where, by the absorption of water, it swells to a size equal to
or greater than the shell. A new shell membrane is formed which takes
the characteristic shape immediately. This gives the phenomenon of
two shells applied face to face, with the sarcode mass within. While
further development of the shell proceeds, there occurs a thorough
manipulation and reorganization of the nuclear material. The two nuclei

Online LibraryMichigan Academy of Science. CouncilAnnual report of the Michigan Academy of Science, Volume 19 → online text (page 6 of 28)