mud, the rest, expanded like a disc or feather, bears the polyps. An axial
skeleton usually occurs in the stalk. Pennatula,* colder waters ; Renilla,*
warmer seas. The GORGONIID^E (sea fans, sea whips) have an axis of more
firmness, which may be calcareous, and the colony may branch and the
branches anastomose. Here belong, besides many tropical genera whose
names end in < gorgiaj Primnoa* of our colder waters; Isis of tropical
seas, with skeleton of alternating calcareous and horny parts, and the pre-
cious coral (Corallium rubrum, fig. 206) of the Mediterranean, the fishing
for which at Naples amounts yearly to half a million dollars. In the TUBI-
PORID^E, or organ-pipe corals, the separate polyps are enclosed in parallel
tubes united at intervals by horizontal plates. The Helioporce were long
regarded as Hexacoralla because of their massive skeletons with six sclero-
septa. The paleozoic Syringopora belongs near Tubipora, while the
FAVOSITIDJE resemble the Alcyoniidse.
Order III. Hexacoralla (Zoantharia).
The simple tubular tentacles are highly characteristic of the
Hexacoralla, as is the arrangement of the paired septa in sixes as
described above. Yet there are exceptions to this rule. On the
one hand is Edwardsia (common in our colder waters), in which
there are sixteen or more tentacles and only eight septa (fig. 205),
but which exhibits a condition through which the young actinians
pass ; on the other hand in the Zoantharia, Cerianthise, and
Antipatharia the rule of six has undergone extensive modification.
Sub Order I. ACTINARIA (Malacoderma). The sea-anemones are
mostly solitary, without skeleton; with numerous septa and tentacles.
They occur in all seas from tide marks
to the greatest depth. A few are
free, but most are sessile. Except the
colonial Zoanthese all can creep by
the pedal disc. Represented in our
seas by Metridium, Bunodes, Sagar-
tia, Biddium (parasitic on Cyanea)
Halcampa, etc. The Zoantheae have
two kinds of alternating mesenteries
and the individuals of the colonies
are usually incrusted with foreign
matter. Epizoanthus lives symbi-
otically with hermit crabs (fig. 113).
Sub Order II. ANTIPATHARIA.
Six pairs of septa and six (Antipathes)
or twenty-four ( Gerardia) simple ten-
FIG. 213. American sea-anemones. A,
ides (after stimp- tacles; colony with a black horny axis
son, B, Biddium parasiticunt (after
Verrill), C, Bunodes sttlla (after Ver-
rill).
10 calcareous skeleton,
late the Gorgonids.
SimU-
260 CWLEXTERATA.
Sub Order III. MADREPORARIA. This group, the richest in species of
any, is characterized by the great development of the skeleton. Theca,
septa, and usually columella and synapticuli are present, and frequently
costaB as well. Solitary forms are few. Usually they form colonies, fre-
quently of thousands of individuals, bound together by a coenenchym
extending from polyp to polyp over the surface of the coral. A colony
FIG. 214. Fio. 215.
FIG. 214. Astrmigia danae* ; five polyps in various stages of expansion.
FIG. 215. Coeloria arabica. (After Klunzinger.)
FIG. 216. FIG. 217.
TIG. 216. Cladocora ccespitosa. (After Heider.) Relations of coral and flesh.
FIG. 217. Favia cavernosa. (After Klunzinger.)
arises from a single animal by continued fission or budding. When the
division is not complete the animals may form long series with numerous
mouths but with the other parts united, the result being that the surface
of the coral is marked by long winding grooves incompletely separated
theca with sclerosepta, as in the brain corals (fig. 215).
Since but little is known of the soft parts, the classification of the Mad-
reporaria is based upon the coral. Three sections of the sub order are recog-
nized. (1) APOROSA, with compact skeleton. Some, like Caryophyllia
IV. CTENOPHORA. 261
(fig. 208) and Sclerophylla (fig. 207) are solitary. Others, like Oculina,*
branch, and still others form compact masses. Astrangia danae (fig. 214),
the only true coral in New England; Astrcea, the brain corals (Cceloria,
fig. 215, Diploria, Manicina); Cladocora (fig. 216), Favia (fig. 217).
FIG 218. Madrepora erythrcea. (After Klunzinger.)
(2) FUNGI ACEA, or mushroom corals, with no outer wall to the coral. Some
are colonial, others (Fungia) are solitary. A sort of strobilation in de-
velopment. (3) POROSA, with skeleton porous like a fine sponge. Madre-
pora* deer's-horn coral (fig. 218), Porites, Astroides.
Class IV. Ctenophora.
The Ctenophores excel all marine animals, even the medusae,
in transparency and delicacy of tissues; many are so soft that a
strong current tears them, and no attempts to preserve them have
been successful. The body is almost always biradially symmetrical;
i.e., is divided by both sagittal and transverse planes into sym-
metrical halves. Since the longitudinal axis is usually longer than
the others, which are generally equal, the body is usually oval or
pear-shaped. In Cesium the sagittal axis is greatly longer, giving
the animal the form of a band, whence the name ' Venus girdle/
The bulk of the animal is composed of a soft jelly with con-
nective-tissue cells, penetrated in every direction by polynucleate
muscle cells branched at their ends and apparently innervated by
special nerve cells. On the outer surface is a layer of ectoderm,
while in the interior is a system of branched entodermal canals.
At the bottom of a depression (fig. 22 IB, p) at the aboral
pole is a thickened patch of ectoderm, the sense body, which has
considerable resemblance to an otocyst (fig. 222). The thick
sensory epithelium forms a shallow groove, strong hairs which rise
from the edge of the groove arch over it, enclosing a space to be
compared to an incomplete vesicle. In the centre is a spherical
262
C(ELENTERATA.
FIG. 221B.
FIG. 219. Swimming plate and epithelial cushion. (After Chun.)
FIG. 220. Hormiphora plumosa. (After Chun.)
FIG. %%,l.-PleurobracMarho<lodactyla. (After Chun.) A, aboral pole; #, front, C, side
view. MM, sagittal axis ; 7T, transverse axis ; c.adr, radial vessel ; c.ir, inter-
radial vessel; c.pr, right and left gastrovascular trunks; ex, opening of funnel
vessel ; <;, subcostal vessel ; m, ' stomach ' ; mq, paragastric canals ; ?i, ciliated
grooves ; DC, sense body ; o, mouth ; 01% ovary ; p, pole-plate ; r.r 3 , rows of combs ;
sc/i, tentacular pouch ; scfcs, its aperture ; sp, testes ; /&, basis of tentacle ; tg. sc7i,
tentacular canal; ti\ funnel; trg, funnel canal.
IV. CTENOPHORA.
263
mass of otoliths, supported on four bundles of S-shaped agglutinate
cilia. From these bundles of cilia eight bands of thickened epi-
thelium, at first in pairs (fig. 223, ws), later diverging, pass to the
oral pole (fig. 221, r). These meridional bands (so called from
their course) consist in part of ciliated epithelium, in part of the
characteristic ' combs ' which are the locomotor organs, and which
must be regarded as transverse rows of long agglutinated cilia.
The combs (fig. 219) arise from thick epithelial ridges, transverse
to the meridional bands, and are so far apart that the free edges
FIG.
FIG. 223.
FIG. 222. Section of sense body of Cnllianira. A, through the centre ; 7?, excentric ;
d, roof of sensory groove ; /, support of otoliths, o ; p, pigment cell ; se, sensory
FIG. 223. Aboral pole of Callianira bialata. (From Lang.) /, supports of otoliths,
o; PP, pole plate; sfc, sense body; to", openings of gastral funnels; ics, ciliated
bands-
of one comb overlap the base of the next like shingles. In conse-
quence of their fibrous structure the combs are strongly iridescent
and in motion cause a beautiful play of metallic red, blue, and green
over the meridional bands. These combs act like oars and row
the body about. Since the combs begin some distance from the
aboral pole, they are connected with it by means of ciliated grooves
following the line of the meridional bands. Experiment shows
that the sense body is an organ of equilibration and of correlating
the action of the different rows of combs.
The ectoderm gives origin to two more important organs, two
pole fields and two tentacles. The pole fields (fig. 221, p; 223, pp)
are two epithelial patches extending a short distance in the
sagittal axis from the sense body and possibly are olfactory or
taste organs. The tentacles arise, in the transverse axis, from the
264 C(EL ENTERA TA.
bottom of deep tentacular sacs, from which they project as long
cords with numerous lateral branches, and into which they may be
retracted. Tentacles and branches contain an axial muscle, while
the ectodermal coating consists largely of adhesive cells. These
are spherical bodies (fig. 224) covered with a very sticky granular
secretion, and, like a Vorticella, supported on the
end of a spiral stalk muscle. These are used in
capturing prey.
The ectoderm also forms part of the gastrovascu-
lar system. It turns inward at the mouth situated
at the lower end of the chief axis and lines the
large space commonly called stomach (fig. 221,
m) but which corresponds to the oesophagus of the
Actinozoa. At the aboral end of this stomach
begin the true entodermal portions, the so-called
FIG 224 Adhesive f unne l s > an( l from them the canals distributed
phora f (Aner through ^ ne j 6 ^ t * ne various organs. Two
Samassa.) (rarely four) funnel canals run to the aboral pole
and empty (fig. 223, to) near the sense body; a second pair, the
paragastric canals (fig. 221 B, mg), which run parallel to the
03sophagus, end blindly. The perradial canals (c.pr) proceed out-
ward from the funnel, and besides giving off a canal to the tentacle
(tg) each divides dichotomously twice, first into interradial and
then into adradial canals, each of these last connecting with a
meridional vessel running just beneath a row of combs, nourishing
them as well as the gonads. The gonads consist of two bands, one
male, the other female, running in that wall of the meridional ves-
sel nearest to the combs. In spite of their position they are
apparently ectodermal in origin.
These gonads are regular in distribution, those of two vessels
which are nearest each other being of the same sex. The eggs and
sperm pass out through the gastrovascular system.
The few species of the group are divided into the TENTACULATA,
with tentacles, and the NUDA, without. To the first belong the CYDIP-
PID^E, with pear-shaped bodies (Pleurobrachia* on our coast, fig. 222), and
Hormiphora (fig. 221); the LOBAT^E (Mnemiopsis,* Bolina*), with lobes;
and the band-like CESTID^E (Cesium, the Venus girdle) of the warmer
seas. The BEROID.E (Beroe, Idyia*}, with wide mouth, belong to the
Nuda. The small creeping forms, Cceloplana and Ctenoplana, are supposed
by some to form a transition to the Turbellaria.
SUMMARY OF IMPORTANT FACTS. 265
Summary of Important Facts.
1. The CCELENTERATA (together with the Echinoderma)
were formerly called Radiata because in most a radial form of
structure is present; in the higher groups this can be transformed
into biradial or even bilateral symmetry.
2. The Coelenterata are sometimes called Zoophyta (animal
plants), from their appearance and their attachment. In many
the resemblance is heightened by their formation of plant-like
colonies by fission and budding.
3. The name Coelenterata was chosen because they have but
one system of cavities, a simple or ramified digestive sac, repre-
senting at once the alimentary tract and the as yet undifferen-
tiated body cavity.
4. This ccelenteric apparatus is called the gastrovascular sys-
tem because its branches distribute nourishment to all parts and so
perform the function of blood vessels.
5. The reproduction is either sexual or asexual, very frequently
cyclical (alternation of generations).
6. The animals are provided with nerves, muscles, and sense
organs and possess marked sensibility and mobility.
7. Especially characteristic are the tentacles and small nettling
organs, the cnidse, in special cells.
8. Nearly all histological differentiation proceeds from ectoderm
or entoderm, since the mesoderm (mesoglcea) plays but a subordi-
nate role and usually functions only as a support.
9. Four classes Hydrozoa, Scyphozoa, Anthozoa, and Cteno-
phora are recognized.
10. In HYDKOZOA and SCYPHOZOA there are usually two
alternating generations, the sessile asexual polyp and the free-
swimming sexual medusa.
11. The hydroid polyp and the craspedote medusa are charac-
teristic of the HYDROZOA.
12. The hydroid polyp is a two-layered sac of ectoderm and
entoderm, a supporting layer and a circle of tentacles. In the
colonial forms there is usually a cuticular envelope, the perisarc,
secreted by the ectoderm.
13. The craspedote medusa is bell-shaped, with smooth bell
margin, its aperture partially closed by a diaphragm-like velum;
the gonads are ectodermal.
14. The medusae arise by lateral budding from the hydroid.
15. If the medusa remain attached to the parent as a sporosac,
266 C(ELENTERATA.
alternation of generations is replaced by polymorphism; it can
entirely disappear with the total loss of either hydroid or medusa.
16. The scyphostoma and the acraspedote medusa are typical
of the SCYPHOZOA.
17. The scyphostoma differs markedly from the hydroid polyp
in the presence of four longitudinal gastric folds or septa (taeniolge).
18. The acraspedote medusa lacks a velum, has a lobed umbrella
edge, gastral tentacles (phacellse), and entodermal gonads.
19. The medusa arises from the polyp by terminal budding
(strobilation).
20. Alternation of generations rarely is lost, and then only by
suppression of the scyphostoma.
21. The ANTHOZOA have only one form, the coral polyp; it is
distinguished from the hydroid polyp by the ectodermal oesophagus,
the radial septa reaching the oesophagus; the well-developed
mesoglcea and the gonads which, arising from the entoderm, early
migrate into the mesoglcea.
22 k . Most Anthozoa are colonial and produce a skeleton usually
of calcic carbonate, but sometimes of l horny ' substance.
23. The skeleton may be either axial or it may extend over the
individual polyps (cortical skeleton).
24. The living Anthozoa are divided according to the number
of septa into Octocoralla and Hexacoralla. To these are added
the fossil Tetracoralla.
25. The Hexacoralla have numerous tubular tentacles and six,
or a multiple of six, pairs of septa.
26. The Octocoralla have eight single septa and eight feathered
tentacles.
27. The CTENOPHOKA are always free-swimming and have a
large mesoderm with numerous muscle cells.
28. Nettle cells are absent, and are replaced by adhesive cells.
29. Most characteristic are the eight meridional rows of
' combs ' whose motions are controlled by a common organ, the
sense body, constructed like an otocyst.
30. The digestive tract consists of an ectodermal oesophagus
and a branching system of entodermal vessels.
PL A TUELMINTHES.
267
PHYLUM IV. PLATHELMINTHES (FLATWORMS).
This group is well characterized by the name. AVith few
exceptions (rhabdocceles, many trematodes) the nearly flat ventral
surface and the slightly arched back are closely approximate and
pass with a more or less sharp margin into each other. In many
cases the ventral surface is distinguished by its lighter color. In
all the bilaterally symmetrical body is composed of a solid paren-
chyma, a mass of connective tissue traversed by muscle fibres, in
which the various organs alimentary tract, nerves, excretory and
reproductive organs are imbedded. In the lower forms the di-
gestive system is markedly like that of the co3lenterates ( Actinozoa,
Ctenophora) in that there is but a single opening and this leads by
an ectodermal oesophagus (stomodaeum) to the interior. In para-
sites the digestive tract may be lost. The skin is a one-layered
epithelium, sometimes ciliated, sometimes protected by a thick
cuticula. Inside this comes a muscular layer (fig. 225) in which
FIG. 225. Transverse section fright half) of a Planarian. ri, vitellaria; dv, dorso-
ventral muscle fibres; e, ectodermal epithelium with cilia; {/, gastric diverticula;
7), testicular follicles ; lm, longitudinal muscles (dots, in section) ; n, lateral nerve
cord.
longitudinal muscles are always present, and in addition frequently
circular and oblique muscles, as well as those passing from dorsal
to ventral surfaces. The nervous system (fig. 228) consists of a
pair of ganglia (' brain') in front of (i.e., above) the oesophagus
and longitudinal nerves leading backwards from it. The excretory
organs (fig. 226) are composed of a series of tubes, the protone-
phridia or water- vascular system/ which branch and ramify the
parenchyma. In most the sexes are united in one individual and
the reproductive organs take up considerable space. There is a
small paired or unpaired ovary and vitellaria, usually paired and
branched. The eggs arise in the ovary, and to these are added
nourishment in the shape of cells (abortive ova) rich in yolk from
268
PL A THELMINTHES.
the vitellaria. At the point where oviducts and yolk ducts unite
a single egg cell together with several yolk cells are united into
an oval body the compound egg protected "by a shell secreted
by special glands (fig. 227, A). This forms only an apparent
exception to the rule that the egg is but a single cell, for the
development shows that only the egg cell takes a direct part in the
FIG. 226.
FIG. 227.
FIG. 226. Excretory system of Cercaria. (After Albert Lang.) ft, limb of bladder ;
b', same with urinary concretions; cc, collecting canal; cs, canals of ventral
sucker; cv, collecting vacuole; e, eye; ep, excretory pore; J, lumen of tail; os, oral
sucker ; vs, ventral sucker.
FIG. 227. Eggs of Dtatomum nodulosum. (After Schauinsland.) A, before develop-
ment; U, later, the yolk broken down, d, yolk cells ; ei, egg cell ; eh, ectoderm ;
en, entoderm ; p, pigment spot.
formation of the embryo and is the true ovum, while the yolk cells-
break down and furnish food to the growing embryo (fig. 227, B).
Class I. Turbellaria.
The Turbellaria are small, only a few being measured by inches,
while many are almost microscopic in size. The name Turbellaria
has reference to the currents produced by the ciliated ectoderm
which covers the body, the cilia arising from the single layer of
columnar epithelial cells (fig. 58). This ectoderm serves at once
for motion and for respiration. Most species are aquatic (fresh
water or marine), only a few land planarians living in moist earth.
In the water they either creep slowly over stones or plants on
their ventral surface, or they swim freely. In swimming the larger
species progress by undulations of the body, the smaller by means
of the cilia.
/. TURBELLAR1A.
269
The alimentary canal (fig. 228) consists only of oesophagus
(pharynx) and mesenteron, the latter terminating blindly since no
intestine or anus is present. The mouth is on the lower surface,
at some distance from the anterior end, being occasionally in the
middle or even behind the middle of the body (fig. 231). It
leads into the muscular oesophagus, which is frequently enclosed
in a special sheath and then can be protruded like a proboscis.
FIG. 228.
FIG. 229.
FlG. 228. Digestive and nervous systems of Syncoelidium pellucidum. (After
Wheeler.) a, alimentary tract ; 6, brain ; In, longitudinal (ventral) nerves ; m,
marginal nerve ; pi, longitudinal nerve of pharynx ; pi\ ring nerve of pharynx ;
<n, transverse nerve ; w, uterine ostium.
FlG. 228.Pulychcerus caudatus. (After Mark.)
The mesenteron, of entodermal origin, varies greatly in shape, its
modifications being made the basis of division of the class into
orders. In the Polycladidea there is a central portion from which
numerous branched caeca are given off; in the Tricladidea there
are three main trunks, each with lateral caecal diverticula; while in
the Ehabdocoelida the digestive tract is a simple rod-like sac, in
some cases ( Acoela) without internal cavity. The supra-oesophageal
ganglia always lie at the anterior end of the body, which is most
sensitive, and may be produced into feeler-like processes. This
270 PLATHELMINTHES.
region usually bears two or more simple eyes, and in a few a single
otocyst.
In many Turbellaria nettle cells, like those of the Ccelenterata,
occur in the skin. Much more common are the rhabdites, small
rods which arise in epithelial cells which sometimes project like
glands into the mesoderm. Those rhabdites occur in the shiny
tracks which the animals leave in creeping.
The hermaphroditic sexual organs (fig. 73) and the excretory
system vary considerably in the separate orders and families. The
eggs are usually very large and are fastened by a stalk to water
plants. Many species form a sort of cocoon, containing a few eggs
and numerous yolk cells. In the marine species a free-swimming
larva (fig. 230) with lobe-like processes may hatch from the egg.
-En
FIG. 230. Larva of Stylochus pilidium. (From Korschelt-Heider, after Gotte.) D,
enteron ; En, remains of entoderm cells ; -S, oesophagus.
This larva, by a metamorphosis, is converted into the creeping
adult. Not infrequently besides the sexual asexual reproduction
occurs. The Microstomidge and some Planarice are capable of
transverse division, and, when well nourished, by rapidly repeated
divisions will form chains of individuals arranged in a row, separa-
tion taking place gradually. For each posterior individual a new
brain and a new oesophagus are formed (fig. 58). The Turbellaria
possess the power, to a marked degree, of reproducing lost parts,
which makes them favorites for regeneration experiments.
In a few Turbellaria there is a noteworthy condition of the digestive
organs. The pharynx connects with an entodermal syncitium, a proto-
plasmic mass, without lumen, containing nuclei in which, as in the pro-
toplasm of a protozoan, the food is digested. This entoderm is hardly
//. TREMATODA.
271
marked off from the mesoderm, but it is a question whether these l Accela '
are primitive or degenerate.
Order I. Polycladidea.
Marine species of considerable size, in which the digestive caeca spring
from a central chamber. Species of Leptoplana and
Stylochus on our shores. Thysanozoon, Europe.
Order II. Tricladidea.
Alimentary canal with three main trunks, an anterior
unpaired and a pair of posterior branches, arising from
the pharynx. These trunks bear lateral caecal branches.
Among the marine genera are Bdelloura * and SyncoR-
lidlum * (fig. 229) (parasitic on Limulus), Gunda,* Poly-
clicerus * (fig. 229); in fresh-water occur Dendrocoelum*
Planaria* and Polyscelis* Phagocata * with divided
pharynx. The land planarians (Bipaliiun,* 10 or 12
inches long) are tropical, but have been introduced
into greenhouses in various parts of the country.
Order III. Rhabdoccelida.
Small, even microscopic, in size, and recalling in
habits and appearance the Infusoria; alimentary canal
rod-like, without branches. Monops* and Monoscelis*
marine. The fresh-water MICROSTOMID.E reproduce
almost exclusively by fission, so that sexual individuals
are rare.
Class II. Trematoda.
These are exclusively parasitic, some living on the skin or
gills (ectoparasites) or in the interior of other animals (entopara-
sites). In structure they are closest to the triclad Turbellaria,
from which they are especially distinguished by characters the
direct result of their parasitic life. Thus they have lost the cilia
or these only appear in the aquatic larval stages. On the other
hand they are armed with structures derived from the skin
suckers and hooks for adhesion to the host. The suckers are
shallow pits of columnar epithelium, lined with cuticle and fur-
nished with a thick muscular layer which by its contraction increases
the lumen of the sucker, the edges of which are closely applied to
the host. At least one such sucker is present; if but one or two
(entoparasites), one is at the anterior end (oral sucker) and sur-
rounds the mouth, while a second larger sucker may occur near the
month (fig. 232), but may be (Amphistomum) at the posterior end.
In the ectoparasites there are a pair of anterior suckers near the
mouth; at the posterior end a single sucker, or a number of suck-
ers or hooks or both on a sucking disc (fig. 234).
FlG.231. Gundn loba-
ta. (After Schmidt.)
<7, cerebral ganglia,
with eye spots ;
o, mouth (entrance
to long pharynx);
p, genital pore with
male organs be-
hind, female in
fron t .