luted tube, and the external opening (fig. 69). In many instances
(Oligochaetes, some Polychaetes) the nephrostome is in one somite,
the external opening in the succeeding. The nephridia also usually
serve as genital ducts, carrying away the reproductive cells, which
HI. ANNELIDA: CH^TOPODA.
always arise from the ccelomic epithelium. In the Oligochaeta
(fig. 286), besides the nephridia in the genital segments special
oviducts and vasa deferentia occur which are usually regarded as
Of the many modifications of nephridia only a few can be noticed here.
Occasionally there may be more than one pair in a somite, or they may
have more than one nephrostome. Again, they may be lacking from more
or fewer somites. In many Oligochsetes they may empty into the anterior
or posterior ends of the digestive tract. In many (Glycera, Hesione,
Nephthys, Goniadd) the internal ends of the nephridia are branched,
the branches being closed by * solenocytes,' tubular cells bearing an internal
bundle of cilia.
In many marine annelids there occurs a metamorphosis in which
pelagic larvae occur. These, in spite of their many modifications,
are comparable with the < Loven's larva/ the trochophore already
FIG. 278. .4, larva of Polygordiu*; B, same changing to segmented worm. (After
Hatscnek.) a, anus; Ten, excretory organ; mes, segmented mesoderm.
described (p. 306). The differences largely consist of modifica-
tions of the ciliary apparatus; the number of bands may be
increased (polytroche larvae), or a single band may occur at the
middle (mesotroche) or at the end (telotroche) of the body. The
larva becomes a segmented worm by the hinder end of the larva
growing out and dividing into segments (fig. 278). In this
jointed portion the coelom arises as a new formation, divided from
the first into separate chambers. The nephridia also arise de
novo, independent of the protonephridial system, which is often
called head kidney because the chief part of the trochophore forms
the head of the adult.
The fresh-water annelids develop directly, but the embryos pos-
sess a reminiscence of an earlier larval life in that the head lobes are
very apparent and contain protonephridia, which leads to the con-
clusion that these animals earlier had a metamorphosis. From the
resemblance of the trochophore to the Rotifera the farther conclu-
sion is drawn that the annelids have descended from Rotifer-like
ancestors, the body cavity, nephridia, blood-vessels, and ventral
nerve chain being new formations.
Besides sexual reproduction many fresh-water and marine
species may reproduce asexually, this being rendered possible by
the great homonymy of the segmentation. By rapid growth at
the hinder end as well as at a more anterior budding zone numer-
ous somites are formed which separate in groups from the parent
to form young worms. In some cases the formation of new somites
FIG. 279. Budding in Myrianida. (After Milne-Edwards.) The sequence of letters
shows the ages of the individuals.
may take place more rapidly than the separation, the result being
chains of worms (fig. 279).
By a combination of sexual and asexual reproduction a typical alter-
nation of generations occurs, the origin of which receives light from the
following facts: In many polychaBtes which reproduce exclusively by the
sexual process the sexless slowly-moving young (atoke) at sexual ma-
turity becomes so altered in appearance as to have been described under
another name. It becomes very active in its movements, and the hinder
III. ANNELIDA: CH^ETOPODA.
somites, which contain the sexual organs, develop special bristles and para-
podia (fig. 284, A). Thus many species of Nereis pass into the * Hetero-
nereis ' stage. In other Polychaetes the sexual part (epitoke) separates
from the sexless atoke portion and swims freely, while the atoke produces
new epitokes. In the Samoaii Islands Eunice viridis reproduces in this
way, the epitokes coming to the surface at certain times in incredible
numbers, forming the 'palolo worm,' a delicacy in the Samoan diet. In
still other species the epitoke regenerates the head and thus becomes an
independent generation. Syllis and Heterosyllis are thus related. The
AutolytidaB furnish the most complication. Here the atoke, by budding
as in Myrianida, fig. 279) forms chains of dimorphic individuals which
later separate. The individuals of male chains were formerly described as
* Polybostriclms,' 1 the females as ' Sacconereis." 1 This same homonymy ex-
plains the regenerative powers of many worms. Thus if certain earth-
worms be cut in two, they will continue to live and will reproduce the lost
Another important character of the Chaetopoda is the posses-
sion of bristles or chaetae. These arise in special follicles, singly
or several in a bunch, of which usually there are four right and
left, dorsal or lateral and ventral in each somite. Each follicle
(fig. 280) is a sac of epithelium opening on the surface and having
at the base a special cell for the development of each bristle. The
developed bristles project from the follicle and, moved by appro-
FIG. 280. Arrangement of a bristle in an Oligochaete. (After Vejdowski.) e, epithe-
lium; rm, iw, circular and longitudinal muscles; w, muscle of the follicle; b,,
chaeta follicle, its chaeta in function ; b a , follicle for replacement, the formative
cell at its base.
priate muscles, form small levers of use in locomotion. Their
numbers, shape, and support are of much systematic importance.
Order I. Polychaetse.
The Polychaetae owe their name to the fact that each group of
"bristles contains many chaetae; but more important is that the
bristles of each side are supported by a fleshy outgrowth of the
somite, the parapodium, in which two portions corresponding to the
bunches of bristles dorsal, notopodium; ventral, neuropodium
may be recognized (fig. 281). This is the first appearance of
FIG. 281. A, head with protruded phaiynx; B, parapodium of Nereis versipedata.
(After Ehlers.) c, cirri; fc, jaws; I, head with eyes; p, palpi; *, tentacles.
true appendages, but they differ from those of Arthropoda in
that they are not jointed to the body nor jointed in themselves.
On the dorsal surface may occur diverse outgrowths, known, accord-
Fia. 282. Ampkitrite ornata* (From Verrill.)
ing to position or function, as cirri, elytra, gills, etc. ; on the head,
palpi and tentacles. The cirri are long processes on the parapodia,
and like palpi are tactile (fig. 281). Elytra are thin lamellse
which cover the back like shingles and thus protect the body.
///. ANNELIDA: CH^ETOPODA. 313
Nearly all Polychsetes are dioecious and undergo a more or less pro-
nounced metamorphosis ; with few exceptions (Manyunkia * from the
Schuylkill, Nereis * in California) they are marine. They are usually
divided according to their habits into fixed (Sedentaria) and free forms
(Errantia), but this classification lacks a morphological basis. The Seden-
taria feed on vegetable matter, usually form tubes of leathery organic
substances, in which foreign matter may be incorporated or which may
be calcified. The worms project their anterior segments from the tubes.
The Errantia often secrete gelatinous tubes in which they can hide, but
they never lose their powers of locomotion, and from time to time leave their
retreats and swim about preying on other animals. Correlated with habits
are differences in structure. In the Errautia the head and trunk are not
very different ; the anterior part of the alimentary tract can be protruded
as a proboscis, and, corresponding to their predaceous habits, is often
armed with strong jaws (fig. 281, A). In the Sedentaria there are no such
pharyngeal teeth, but, on the other hand, there is a greater difference
between anterior and posterior somites. In the
latter the parapodia are weakly developed, and
this part resembles the OligochaBtes in ap-
pearance. The head and beginning of the
trunk (thorax) are richly provided with gills
and tentacles for respiration and the taking of
food (fig. 282).
Sub Order I. ERRANTIA. Predaceous
annelids with strongly armed pharynx. The
EUNICID^E, mostly represented on our shores by
small species, contains some species a yard in
length. Diopatra,* Nothria* The ALCIOPHXE
are transparent pelagic forms with large, highly
developed eyes. The SYLLIDJS usually have
three long tentacles ; Autolytus* Myrianida*
(p. 310). The POLYNOHXE * (Lepidonotus* Poly- projecting at the sides.
noe* (fig. 283), Aphrodite aculeata,* the sea
mouse, 6 inches long) are bottom forms with elytra covering the back.
NEREIDS ; Nereis virens,* the clam worm of all northern seas.
Sub Order II. SEDENTARIA (Tubicola, Cryptocephala). These forms
cannot wander about at will, but live in their tubes. In the SABELLI-
DJE the tube is membranous and there is a crown of gills ; Myxicola*
Chone,* Manyurikia* In the SERPULHLE the tube is calcified and is
closed by an operculum on one of the gills. Hydroides; * Spirorbis,*
forming coiled tubes on seaweed ; Protula* The ARENICOLID2E,* which
burrow in sand, have gills on the sides of the body. The MALDANID^E
(Clymene* Axiothea*) have extremely long segments and build tubes
of sand. The TEREBELLID^E (Terebella* Amphitrite (fig. 282), Thelepus*)
have numerous filiform tentacles and branched gills on the anterior end.
The AECHIANELLID^], which lack bristles and parapodia,
must be placed near the Polychaetae and are usually regarded as very
primitive forms which in structure and development (fig. 273) are
of importance in the phylogenesis of the Annelids. Polygordius. *
FlG. 284. New England Annelids. A, male Autolytvs ; B, Sternaspis fossor ; C, Cis-
tenides gouldii ; Z>, Clymene torquata. (From Emerton and Verrill.)
Order II. Oligochaetae.
The Oligochaetes are almost as preeminently fresh-water and
terrestrial forms as the Polychaetes are marine. They are in
most respects simpler than their marine relatives, apparently the
result of degeneration, which has followed from the more simple
conditions of existence. Eyes are rudimentary or lacking, they
have no palpi, cirri, or tentacles; gills are rare, but most striking
is the absence of parapodia, the bristles projecting directly from
the body wall (fig. 280). The chaetae may be regularly distributed
around each somite (Pericliceta) or gathered on the sides (Megas-
colex) or arranged in four bunches so that in the animal four
longitudinal rows occur. The animals are hermaphroditic, testes
and ovaries lying in different somites. Usually the integument in
the neighborhood of the sexual openings is thickened by the
///. ANNELIDA: CH^TOPODA.
presence of numerous glands, forming a clitellum (fig. 274), which
secretes the egg cocoons. The clitellum also functions in copula-
tion, secreting bands \vhich hold the animals together so that
the sperm from one passes into the receptaculum seminis of the
other. After impregation the eggs are usually enclosed in
Sub Order I. LIMICOLA (Microdrili. ) Mostly fresh-water forms.
The TUBIFICID.E, in consequence of the red blood, when present in large
numbers color the bottom red. They quickly retract into the tubes which
FIG. 285. Aulophorus vagus, in tube of Pectinatella statoblasts. (After Leidy.)
they form in the mud. Tubifex* Petoscolex ; Clitellio irroratus* common
on our seashores. The NAIDID^E are transparent forms living on water
plants which reproduce asexually throughout nearly the whole year.
FIG. 286. Sexual organs of Lumbricus herculeus (after Vogt et Jung); the seminal
vesicles of the right side cut away, hm, ventral nerve cord; foZ, bi\ lateral and ven-
tral rows of setse; di, septa ; ftj, ft s , testes, enclosed in sperm reservoir; o, ovaries ;
ew, oviducts ; sbu, sperm reservoir ; sftj, 2 , 3 , sperm sacs (seminal vesicles) : *t
seminal receptacles; t,, t s , seminal funnels connected with the vasa deferentia;
to, funnels of oviducts; rd, vas def erens.
Z>ero* and Aulophorus* have gills around the anus. ENCHYTILEIDJE ;
Distichopus, Pachydrilus. The DISCODRILIDJE (Bdellodrilus, Nyzobdella)
Sub Order II. TERRICOLA (Macrodrili). Here belong the terrestrial
forms, the earthworms, our species of moderate size, in the tropics large
species (Megascolex australis four feet long). Our species belong to
Lumbricus* Allobophora*; Perichceta* has been introduced from the
tropics; Diplocardia * with double dorsal blood-vessel. Most species agree
in habits; they burrow through the earth, swallowing the humus and
casting the indigestible portions on the surface. They loosen the soil and
are continually bringing the deeper parts to the surface, and thus do great
good. Contrary to oft-repeated statements, earthworms occurred in our
prairies and plains when first broken up by the plow. Details of the
reproductive organs of one species are shown in fig. 286. These vary
greatly and are largely used in classification.
Sub Class II. Gephyrcea.
The exclusively marine Gephyraea are distinguished at the first
glance from the Chaetopoda by the
entire absence of segmentation. The
body is oval or spindle-shaped, circular
in section. The mouth, at the ex-
treme anterior end, is either surround-
ed by a circle of tentacles (fig. 287}
and is retracted together with the
anterior end of the body by internal
retractor muscles, or is overhung by a
FIG. 287. FIG. 288.
FIG. 287. Anatomy of Phascalosoma gouldi (orig.). a, anus; a, anterior retractors
d, digestive tract; g, gonads; m, mouth; n, nephridia; TIC, ventral nerve cord
pr, posterior retractors.
FIG. 288. Larva (trochophore) of JSchiurus. (After Hatschek.) a, anus; d, intestine
hw, postoral cilia; fcra, protonephridia; m, mouth; mes, mesoderm bands with indi-
cation of segments; n, ventral nerve cord; sc, oesophageal commissure; sp, apical
plate; vto, preoral ciliated band.
///. ANNELIDA: GEPHYR^A. 317
dorsal spatulate preoral lobe or * proboscis ' which may be several
times the length of the body and forked at its tip (fig. 289).
Internal segmentation is also lost, septa being entirely lacking.
The nephridia are also reduced in number, at most but three pairs
being present, and in some but a single unpaired organ. They
are sexual ducts, and in the Chaetiferi there are special excretory
organs (fig. 289, g] covered with branching canals opening to the
body cavity by nephrostomes and emptying into the intestine. These
resemble somewhat the branchial trees of the holothurians (infra),
and hence these animals were formerly supposed to bridge the gap
between holothurians and annelids, whence the name (yetyvpa,
bridge) Gephyrsea. The vascular and nervous systems are more
like those of other annelids. The vascular system consists of a
dorsal and usually a ventral longitudinal trunk; the nervous
system of a brain, oesophageal collar, and ventral cord, the latter
without division into ganglia. The relations of the Gephyrsea
to the Chaetopoda are shown by the development. In some
(Chaetiferi) there is a trochophore (fig. 288) from which the worm
arises, as in the Chaetopoda, by growth at the hinder end; this at
first has a segmented coalom and nervous system, the metamerism
being lost later.
Order I. Chaetiferi (Armata, Echiuroidea).
With spatulate preoral lobe, often forked at the tip; at least a pair of
ventral setae; a trochophore in development. Ecliiurus pallasii* in our
northern waters, Thalassema* farther south. In Bonellia there is a
marked sexual dimorphism (fig. 289). The female is 2 to 3 inches long and
has a proboscis 8 to 12 inches long. The male is only 1 mm. long, totally
different in appearance, and lives parasitically in the oesophagus of the
female (fig. 289, B).
Order II. Inermes (Achaeta, Sipunculoidea).
Distinguished by lack of chsetse, the mouth surrounded by tentacles,
and the dorsal and anterior position of the anus. The larva is a modified
trochophore without preoral ciliated band and without segmentation; only
two, sometimes but one, nephridia. Phascalosoma* common on our
shores. Phascolion strombi * builds tubes in deserted snail shells. Sipun-
Order III. Priapuloidea.
No tentacles, mouth with chitinous teeth, terminal anus, no nephridia;
two protonephridia united with the sexual organs and opening either side
of the vent. Development unknown. P?*iapulus, Halicryptus.
Sub Class III. Hirudinei (Discophori).
Three points of external structure clearly distinguish the leeches
from the chsetopods. First, the absence of bristles (except in
Acanthobdella) and the presence of two suckers, one of which occurs
on the posterior ventral surface and is used only for attachment
and locomotion, the other, sometimes scarcely differentiated,
FIG. 289. Bonellia viridis. A, female (after Huxley); J?, male (after Spengel). c,
cloaca; if, rudimentary intestine; 0, excretory organ; i, intestine; w, muscles sup-
porting intestine; s, balls of spermatozoa in B, in A, proboscis (preoral lobe); w,
single segmental organ, functioning as oviduct; vd, nephridium with ciliated
funnel serving as vas deferens.
surrounds the mouth and is used in sucking the food. In locomo-
tion anterior and posterior suckers are alternately attached, the
body being looped up and extended like that of a ' span worm. '
The animals can also swim well by a snake-like motion of the
A second point is the fine ringing of the body, there being
usually many more rings than somites, the primitive segment rings
being divided by secondary constructions, there being three, five,
or even eleven rings to a segment. The middle or one of the
anterior rings is often distinguished by bearing strongly developed
sense organs. As in the earthworms, certain of the somites at the
time of reproduction may develop into a clitellum which secretes the
///. ANNELIDA: HIEUDINEL
A third character is the marked flattening of the body in the
dorso ventral direction (except in Ichthyobdellidae and a few other
forms), the animals thus recalling the flatworms. This may be
the result of the very slight development of the coelom. In most
leeches there is a body (parenchyma, traversed by longi-
tudinal, transverse and dorsoventral muscles in which
the organs are immediately imbedded (fig. 290).
The alimentary tract is provided with paired
diverticula (fig. 291), varying in number in different
species. Between the last and largest pair of these
sacs is the intestine, which opens dorsal to the pos-
terior sucker. The jawed and jawless leeches show
considerable differences in the pharyngeal region.
FIG. 290. Transverse section of Hirudo medicinalis. (From Lang.) dm, Zm, rm, dorso-
ventral, longitudinal, and circular muscles; vi, vd, w, lateral, dorsal, and ventral
blood-vessels, the latter surrounding the ventral nerve cord, ni; h, testes; vd, vas
de^erens; md, midgut; np, nephridial tubule; enp, urinary bladder.
FIG. 291. Digestive tract of Hirudo medicinalis. (From Lang.) a, oesophagus; 6, in-
testine; d,, d a , gastric diverticula.
In the first there are three jaws in the phaynx, semicircular chitin-
ous plates, the free edge of each armed with numerous calcified
teeth (fig. 292). To these are attached two muscles, one to retract
them, when not in use, into pockets, while the other exserts them
and rotates them, causing a triradiate wound from which the blood
flows. This bleeding is difficult to staunch, since glands on the
lips and between the jaws produce a secretion which hinders the
coagulation of the blood. In the jawless leeches a sharp conical
process arising from the pharynx can be protruded from the
mouth, and serves for wounding and sucking. The vascular
system usually contains red blood, and consists, in the Gnatho-
bdellidae, of four longitudinal trunks, a dorsal, two lateral, and a
ventral, the latter surrounding the ventral nerve cord. These are
connected by a complicated system of capillaries.
The nervous system consists of brain and ventral cord, the lat-
ter containing frequently twenty-three ganglia (the first of five
fused, the last of seven). Nerves from the brain go to the eyes.
Eight and left of the ventral cord are the hermaphroditic sexual
organs. In Hirudo medicinalis (fig. 293) there are nine pairs of
FIG. 292. Hirudo medicinalis^ medicinal leech. (After Leuckart.) a, anterior end
with three jaws (fc); 6, a single jaw with its muscles.
FIG. 293. Nervous system, blood-vessels, sexual organs, and nephridia of a leech,
ventral view, ft, testes; hb, urinary bladder; ly, lateral blood-vessel; n, ventral
nerve cord; n/i, epididymis; ov, ovary; p, penis; sc, iiephridia; it, uterus and
vagina; vd, vas deferens; vg, ventral blood-vessel.
(7i), the ducts of which unite to form a vas deferens on
either side (vd). These pass forward, form by coiling a so-called
epididymis (nh) and empty into the median unpaired penis (p).
In the space between the epididymis and the first pair of testes
are the ovaries (ov) and oviducts and an unpaired vagina (u). The
nephridia (17 pairs in this species) are complicated and are pro-
vided with bladder-like expansions.
That the Hirudinei are true annelids and not segmented Plathelminthes
is based upon the view that their coelom is reduced by ingrowth of paren-
chyma and altered to canals connected with the vascular system. At
any rate the ventral and lateral vessels are to be regarded as remnants of
a coelom. In Clepsine there are the dorsal and ventral blood- vessels of
the Chaetopoda and besides four longitudinal coelomic sinuses connected
by transverse anastomoses. The dorsal sinus encloses the dorsal blood-
vessel, the ventral many of the viscera, among them the ventral nerve
cord. This is also to be regarded as ccelomic, since the nephrostomes con-
nect with it. In most Hirudinei a canal system filled with blood has
arisen from the coelom and blood-vessel, and in Neplielis is in part lacunar
in character. Further relations are shown by Acanthobdella peledina,
parasitic on fishes. This has both blood-vessels of the Oligochsetes, a
IV. POLTZOA. 321
body cavity divided by septa and chsetsd. On the other hand it is leech-
like in other features; two suckers and sexual apparatus on the Hiru-
Order I. Gnathobdellidae.
The jawed leeches include Hirudo medicinalis, once extensively used
for blood-letting but now little employed. Hcemadipsa includes land
leeches, one of the terrors of travelers in the tropics. In Nephelis * the
jaws are soft. Macrobdella * includes our largest native species.
Order II. Rhynchobdellidae.
Without jaws. The CLEPSINID^E mostly feed on snails and fishes.
Clepsine * in our waters. Hcementaria officinalis of Mexico is used for
blood-letting ; H. ghiliani of South America is poisonous. The ICHTHYO-
BDELLID^E, cylindrical, occur in salt and fresh water, parasitic on fishes.
Ichthyobdella,* Pontobdella* marine ; Piseicola, fresh water.
Class IV. Polyzoa (Bryozoa).
In external appearance the Polyzoa closely resemble the
hydroids, so that the inexperienced have difficulty in distinguishing
them. Like them by budding they form colonies which are either
gelatinous or calcareous incrusting sheets or assume a more bush-
like character. Further they have a crown of ciliated tentacles
which can be spread out or quickly retracted. In internal charac-
ters the two groups are greatly different. The Polyzoa have a
complete alimentary canal, with its three divisions, which is bent
upon itself so that the anus lies near the mouth. The central nerv-
ous system lies between mouth and anus, and the single pair of
nephridia empty by a common opening. Beyond this it is diffi-
cult to go, since the two groups of Polyzoa Endoprocta and Ecto-
procta differ so widely that one may doubt whether they belong
together. The Entoprocta have no coelom, and resemble in this
respect the Rotifera; the Ectoprocta are true Coelhelminthes and
by way of Phoronis show resemblances to the Sipunculoida and so
to the Annelida.
Sub Class I. Entoprocta.
The single individuals of the Entoprocta (fig. 294) are shaped
like a wine-glass and are placed on stalks which rise from (usually)
creeping stolons. The circle of tentacles, arising from the edge
of the cup, enclose the peristomial area in which are both mouth
and anus, and between these the excretory and reproductive organs