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THE NATURAL HISTORY, ORGANIZATION AND LATE
DEVELOPJ.ffiNT OF THE TEREDINIDAE.

A Thesis

Pi-esented to the Board of Univei'sity studies
of the Johns Hopkins University for the Decree of
Doctor of Philosophy,

by
Charles P. Sigerfoos, S.E,

al

til q

Contents.

I. Introduction.

II. Methods.

III. Natural History of the "Shipworms".

IV. Organization and Late Development of the "Ship-wontis".

a. The Organization and Metamorphosis of the Larva

b. The General Organization of the Adult.

c. The Shell and the Palettes.

d. The Kantle and the Siphons.

e. The Muscular System.

f. The Respiratory System.

g. The Circulatory System,
h. The Alimentary Canal.
i. The Neiwous System.

j . Tlie Kidneys.

k. The Reproductive Organs.

1. Conclusions.

V. Bibliography.

VI. Explanation of Figures.

Introdncv ion.

-00-

My work on the "Ship-v/omis" v/as first suggested by
Professor \Y. K. Brooks, His constant interest and sympathy
throiighovit my stay at the Johns Hopkins Universitj/ have been
of great help to me and it gives me great pleasure to ac-
knowledge my indebtedness to him. My material vms collected
at Beaufort, North Carolina, during tlie summers of 1S95 and
1396 » and my study '.js been continued in tlie laboratory in
Baltimore. To the Authorities of the Johns Hopkins Univer-
sity I am under deep obligations, both for the privileges
of the marine laboratories at the seaside, and for facili-
ties for Vi'ork in ihe laboratory in Baltimore.

The " SI: ip- worms" were favorite objects for study
during the eighteenth century, on account of their great
' damage to the dykes of Holland in 1733 and subsequent years.
The first modern observations wore those of Valisnieri (1715)
and Deslandes (1720) After 1733, came Mossuet, J. Roussot,
and especially Godfrey Sellius. These observers seem to
have boon unaware oi' the ancient observations mentioned by
Theophrastus , Pliny and Ovid, and it was supposed the "Ship-
v^onns" were natives or India, wiience they- •■ '^ '-^•^'-! brought

by shipi)inG in modern times. It was Godfrey Sellius 'jho
first recognized the Molluscan characters of Teredo, but
those were not used by Linnaeus, wlio grouped it along v/ith
Serpula and Dcntalivun. Cuvier and Lamarck adopted the viov/
of Sellius, and uince their time the group has been put in
its proper place.

The first reliable observations on the anatomy of
the " Iiip-wonns" were those of Deshayes, who gave a ni:imbor
of ' jautifully executed plates to Teredo in his "Mollusques
d'Algerie", 1846. Kov^ever, like most of the plates of this
great v/ork, they are difficult to study and interpret. Sup-
plementing the work of Deshayes is that of Quatrefages , (14)
who began and completed his observations before he had ac-
cess to the published results of Deshayes. This "Memo ire
sur le Genre Taret (Teredo, Linn.)" is the one usually cited
at the present time, although the paragraph with which Quatre-
fages prefaces his paper is aLaost as applicable now (with
slight changes in the wording) as v/hen it was written in
1849. "Naturalists up to the present time", he says, "have
strangely neglected Ter'^r-''.o. This is not the place to review
the anatomical researches of the last century whicii are fil-
led v/ith errors excusable by the state of science of that

period. But it is surprising that a mollusc with such re-
markable exteiTial cliaracters has not been the object of any
special rosearchf rom tlie foundation of comparative anatomy
up to the present time. It is necessary to come to the year
184G to find a naturalist who has taken for the subject of
his observations this mollusc so unfortunately celebrated.

Since the appearance of the memoir of Quatrefages ,
no detailed accoiont of the whole organization of Teredo has
appeared. Only in comparative treatises has it been taken
up. The principal of these are the papers by Grobben (4) on
the pericardial glands in Lamollibranchs , by Iv'enegaux (ll)on
the circulatory system in Lamellibranchs ; and by Pelseneer
(14) in :iis extensive comparative studies in the group.
Grobben first observed the anterior adductor muscle in Tore
do and proved the Teredinidae to be dimj'arians. Aside from
this point, the figure of Teredo thai he gives is v/holly un-
reliable. J.'enegaux attempted to establish the homologies of
the aortae, and Pelseneer described the visceral ganglion
and related structures. I shall have occasion to refer to
these papers in special i)arts later, and it v/ill be seen
that the comparative method of study is not alvirays satisfac-
tory, ii' the examination of special foi-ms be not made witli

sufficient care. My results differ from all oi' tJiese.
Unfortunately the first tv/o do not state the species on
which they worked, and so I cannot state that where my
observations differ from theirs, they were in error, though
there is such great uniformity of organization in the va-
rious species, that we may expect only differences in de-
tail in the variou.s types.

My observations have been based chiefly on Kylatrya
f imbriata , Jeffreys , and unless otherwise stated, this is
the form described and figured. Specimens of this species
I have had in all staces of development from the nev/ly at-
tached larva to tlie adult. I have also studied Teredo noi*-
vegica, Spengler, and T. navalis, Tanne and vAhere these
are essentially different or more favorable for descrip-
tion, they have been used. In general, where "Teredo" is
used as a popular term, it applies to Xylatryaas well as
to the species of Teredo, in a strict sense.

The object of my study of the "Ship-worms" has been
tv^o-fold. In the first place, I have endeavored, by the
use of modern methods, to give a detailed account of the
organization of this highly specialized Lamellibranch and
to correct the errors that have heretofore existed in the

clGScriptions of it. In lhj second place, by tlie study of
young stages, I liave been able to trace the transformation
of the typicv.l Lamollibranch larva into the highly spe-
cialized "Ship-v.'orm".

I have also traced the early embryology on the arti-
ficially fertilized eggs of X. fimbriata and T. norvegica,
in both of v;hich the eggs are laid free into the water.
Stages later than the typical Lamellibranch veliger raised
in aquaria, I have not been able to observe. The interme-
diate stages, betvTeen these and the newly-attached larva,
I hope to observe on the larvae of some viviparous species
at a fixture tine, so as to complete my study of the devel-
opment from the egg to the sdult.

II. METHODS.

My presorved material was collected and prepared for
study as follows:- By hanging boxes and otlier structures
of wood in the water at Beaufort , I was able to obtain all
stages from the newly-attachod larva to ". .ip-v;orms" four
inches long, v/ith adult organization. The yoiongest stages
were collected from the surface of the vrood. Later stages
were dissected ov^t of the wood into wtiich they had bored.
Early stages were narcotized with cocain and aftervmrds
fixed v;ith mercuric chloride. Specimens 1 cm. or more in
length v;ere treated as follows: They- vrere exposed quick-
ly and immediately a quantity of Hermann's solution was
dashed upon them. This kills them instantly, before they
have had time to contract appreciably. They were then im-
mediately immersed in mecuric chloride or Perenyis' solu-
tion for fixation. After '.vashing in weaker alcohols, spe-
cimens were preserved in 90^ alcohol. The early stages
were stained in Kleinenberg's hematoxylin. For later
stages, the best results were obtained with borax-carmine,
follov/ed by Lyons blue. For the examination of whole ob-
jects, the best results were obtained by stainin;: in a
weak solution of borax- cannine in acid {1-^"'''' CI. )70', al-

cohol , v/I;ich decalcifins aa v/ell as stains. The Tigiures
have all been rlravm with the aid of a Zeiss camera lucida.
In some car.-^s, as in the series of transverse sections of
the adult (firrs. :13-Zb) , they have been "touched up" af-
terv/ards. However, in no case have thejr been essentially
modified and are in no wise diagrams. The figures of ad-
ults have been made from specimens about ten centimeters
long, vfhich I had raised, and v^hich were killed perfectly
extended. The siphons, however, have been filled in from
life, or from preserved specimens tliat had been narcotized
before killing. In larger specimens the body as a vfhole ,
and the various orr;ans are somewhat more elongated, but
the relations remain the same as in yoi^nger specimens.

8

III. IIATURAL HISTn^v op THE "SIIIP-WORI'.^S" .

Any wooden structures that one may examine at Beau-
fort, which have been in the \rater for some time and un-
protected, are alv/ays foimd infested with "Ship-wonns ".
These are of three species, which Professor V/. H. Dall has
kindly identified for me as Xylotrya fimbriata, Jeffreys,
Teredo navalis, Linne and T. norvegica, Spengler. X. fim-
briata and T. norverica are very abundant, v/hile T. nava-
lis is fouj^d but rarely. X. f i^^^r^ •'tPi, is the most abund-
ant of all, and is found everywhere. It may attain a
length of tv/o feet, though where it grows in large niunbers
it is 30 crowded that specimens are oftener less than a
foot in length. T. norvegica I have found mostly in the
heavier piles of wharves, v/here specimens may attain the
great size of four feet in length and an inch in diameter.
T. navalis I have found very sparingly, not over a dozen
specimens among the thousands of individuals I have exam-
ined. These in all cases were small specimens, from which
it seems that the habitat at Beaufort is not favorable for
them, and is more favorable for the other tv/o species
v/hich fully occupy all of the available places for "oliip-

worm" life. Tho v/ater contains a hi£;h percentap;e of salt,
and the warm season is lone, and these factors may accoiint
wholly or in part for the absence of T. navalis.

Of tho thousands of yoimg specimens (under four
inches in length) I l:ave taken from boxes, all were of
X. fimbriata except four specimens of T. navalis. These
were observed in June, July and early in August. Whether
tlie absence of T. norvep:ica was due to unfavorable loca-
tions, or the season for attachment is different from that
of the other two species, I was not able to determine.

Breeding Habits. As is well known, some species of Tere-
do retain their eggs in the gills during the embryonic
development. This is true of T. navalis, and even the
small, (an inch or more ) specimens of this species I have
taken, have usually had embryos in various stages of devel-
opment. On the other hand, I have found that the eggs of
the other two species are laid free into the water. If
species of T.rorvegica be taken from their tubes, they
soon begin to extrude their sexual p^'oduct;:, if th'^se be ma-
ture. The eggs and sperm are exti'uded from the anal or
exhalent siphon in a slow, steady stream, vMiich continues

10

as long as the sexual oi*{;an contains ripe sexual product:^.
X.ylotrya fimbriata I have observed but rarely extruding
its sexual products: in this manner, out why ihurc is a dif-
ference in this habit I have not determined.

In accordance with thoir free development in the
water, the eggs of the "Ship-worm" are verj' small and very
numerous. Wiile they vary somewhat in size, they have an
average diameter of somewhat less than 1-20 ram. Very
large specimens may lay p;reat nvimbers of eggs at one time;
in one case I estimated the number laid by a large female
of T.norvegica at one hundred million. The sperms are
very minute, and mucih more numerous than the eggs. The
eggs of both species that lay their eggs free may be fer-
tilized artificially, and pass the early stages of devel-
opment with great liniformity and rapidity in aquaria. The
eggs when first laid ai-e of irregular shapes. They soon
become spherical, and if fertilized, the polar bodies are
soon extruded and segmentation begins. Development is
ver;^ rapid and on v/arm days, the embryos become free-swim-
ming within three hours after the eggs are laid. Within
a day the shell has been formed and the typical Lanolli-
branch veliger stage i ^- i-eached. ^r-'-ond tliis stage they

11

do not develop in aquaria, tlioiigh thoy may live for days
afterwards. Ilatschek has observed (o) that the Vivipo-
rous larvae of a species studied by him (T. navalis?) are
almost alv/ays present in only -i few stages, and that trans-
itional stages are but seldom found. It seems probable
that the free-living larvae of Xylotrya and T. norve";ica
attain one of these stages within a short time, and that
the unusual conditions in aquaria prevent their advance
beyond it.

The mode of life, and rate of development beyond the
early stage attained so rapidly in aquaria, have not been
determined. Y/hat becomes of the larvae that hatch from
the eggs, how and where they live, it is difficult to sur-
mise. Though the developed larvae are settling on wooden
structures constantly, I have not taken them and interme-
diate stages in the tow-net, and v/here they develop I do
not know. However, the rate of growth of the marine La-
mollibranchs is slow, and I think the larvae of "Ship-
worms" that attach must be at least a month old, it may be
more. At this time their development is quite advanced
and their organization complex. (See th.-- description of the
organisation of the larva)

12

The broedinn season o: . irnhriata and i', i>orvGf;ica
seems to extend, tliroxagh the v/arni season. I i.uve round
ripe sexual products of both species i'rom early in May
till the middle of August. At the latter time there seem-
ed no abatement in their development. As v/ill be describ-
ed later, individuals became sexually mature in a month
after they have attached, and those which attach in August
must bear ripe sexual products later in the season, so
that the breeding season seems to extend throiagh the sum-
mer.

Attachment of the Larva.- During its free mode of life,
the "ship-v.'orm" larva has gradually developed into the
typical larva of marine Lamellibranchs. There is a shell
into v/hich the v;hole creature may be wi thdravm foi- protec-
tion; a large svyimming organ, the velum, by means of which
the larva swims freely in the v/ater; a long, active foot,
by means of which it crawls actively over sui'faces. At
the end of this larval development, in fact, the "T'^ip-
worTO"larva is a typical small bivalve, except that it pos-
sesses the svrimming organ.

Throughout the cummer (or at least from t'ay till

13

August! "' ■ ■■ rifort, if one examines unprotected v/ooden
structures submei'iF;ed in the water very small bivalves will
be round crawling actively over t!ie surfaces. These are
very minute and are easily recognized as "Siiip-worm" lar-
vae v/hat have just settled upon the wood. The larva moves
rapidly in search of a favorable place for attachraent, and
this is usually in some minute depression or crevice in
the wood, though it may also become attached to perfectly
smooth surfaces. It seems to possess no organ of special
sense for the purpose, and yet, it is able to determine
what places are favorable for its futuji'e life, and to
avoid those which are not. Once it lias chosen a point for
attachment, it tlirows out a single long byssus thread,
v/hich secures it at the surface of the v/ood, and soon los-
es its velum, so so that it can no longer lead a free life.
Once attached, the larva bo "-ins to clear avmy a place, by
scraping av;ay the surface of the wood with the ventral
edges of its shell valves. Small particles of \rood and
other substances, that are thus formed, are cemented togeth-
er over the larva so as to form a sort of conical covering
for protection. This formed, the transformation of the
larva into the small "L^.iip-worm" begins and progresses rap-

14

idly. The foot becomes a pestle-shapod orr;:an which assists
the sliell in buiTowing. The sliell valves lose their power
of opening at tlio ventral side, 'anu by tivj (iovelopment of
knobs on the ventral and dorsal portions of either valve,
they are able to swing on each other at ri,p;ht angles to
the former direction. Meanwhile the shell gapes at both
anterior and posterior ends, for the protrusion of the
foot in front, and the siphons, and later the body, be-
hind. And on the anterior edges have been formed the small
teeth which at this and later stages are the mechanical
agents by which their possessor bores into the wood. This
transformation has taken place v/ithin two days fi"om the
time the larva has settled, and afterwards the animal rap-
idly becomes a "S!iip-wonn" , enlarging its buri'ow in the
v;ood as it increases in size.

Rate of Growth within the V/ood.- The "r-hip-worm" in its
larval stages develops but slov/ly, but once in the wood,
it grows with remarkable rapidity. During its free life,
most of its energies seem devoted to active locomotion and
development; after attachment, it leads a sedentary life
and its c^o'irth is correspondingly rapid. The newly-attach-

15

ed larva is somewhat less than .25 mm. lonr. In 12 days
it has attained a length of about 3 mm.; 16 days, 6 mm.;
20 days, 11 mm.; ?0 days, G3 mm., and S6 days, 100 mm. It
is thus seen that v/ithin two v^ecks from the time it has
settled, the "Ship-worm" has increased hundreds of times
in size, and in five weeks, thousands of times. Within
tv;o v;eeks it has changed to a real "Hhip-worm", and even
in a month specimens may contain ripe sexual elements,
thougli normally these are retained till larger quantities
of sperm and eggs are stored for extrusion at one time.
I shall describe later what appears to be a change of sex
from males to females, the male sex being developed in
yoting specimens. I have found males four v/eeks old gorged
with ripe sperms, and in every way adult.

The ages of larger specimens I have been able only
to estimate, from the time the piles and other \vooden
structures from which they were taken, had been in the wa-
ter. In one case I took specimens four feet long and an
inch in diameter at the anterior end, from piles that had
been in the water less than two years. This was in July,
and in this case it seems the "\ orms" had entered the wood
not earlier than the spring of the preceding year, and

16

lience wore little ii" any over a year old.

The rate of growth seems to depend but little if at
all, on the hardness or kind of wood. It is well knovm ,
"Ship-worms" penetrate all kinds of wood, whether it be
soft white line or hard oak. In India there are types
that bore into stiff clay. None of our species adopt such
a habitat, so far as I know. But I have found small, ab-
normal specimens of Xylotrj''a in very rotten wood, and I
take it that their' abnormal character v/as due to unusual con-
ditions. In this case they v/ere associated with Xylor'haf'a
dorsalis and Pholas dactylus. However, in wood proper, I
have observed that they grow quite as rapidly in hard yel-
lo.Y pine as in soft white pine; so that the rate of growth
seems conditioned by food supply, and not by the ability
of the animal to form its burrow.

Protective Adaptations. - The life of the "Ship-worm" in
the wood has led to profound changes in tiie character of
its external parts and its means of protection. As the
"V/orm" enters, the posterior part of the body projects
more and more beyond the shell v/hich loses its protective

17

character, to take upon itself the sole purpose of burrow-
ing. In specimens 2 mm. lonr, , the shell is still a quart-
er of the length; in specimens four feet long, the shell
is an inch or less in length. With the loss of protection
by the shell, other means are acquired. In a general way,
the burrow offers the i)rotection afforded by the sliell in
other forms. But the very delicate tissues of the mantle
wovild be injured by the rough surface of the wood, and so
as the body elongates, it secretes around it a constantly
thickening calcareous tube, v/hich lines the v/hole burrow
except the anterior end, v/here the mantle is somewhat less
delicate; and where the tube fades out and the burrov/ is
being constantly enlarged.

When the young "'.Vorm" enters the wood, it penetrates
vertically to the surface, but soon bends its course, so
that within two inches, usually, it becomes straight and
the worm bores with the grain. Individuals that enter the
wood on end, cut across tlie grain from the start, so tliat
their burrows are straight, unless they are turned from
their course by obstructions of any sort. If these are
met, the course is changed so that the burrows may become
very tortuous. When the "J'hip-v/orm" is in danger of bor-

18

ing into the tubes of its fellows, or into otlier spaces,
if its course can bo no longer changed, it contracts the
anterior part of the body slightly, secretes a closed cal-
carooiis lining in front of it, and ceases to burrow furth-
er and to grow. Otherwise, it seems it may grow indefi-
nitely, and it is difficult to predict how large specimens
of T. norvegica might become, were there not adverse con-
ditions to stop tliGir growth.

I believe the calcareous lining of the burrow has
been acquired primarily for the protection of the very
delicate body from the rough surfaces of the wood. But it
serves other purposes also. It prevents the diffusion of
injurious substances into the burrow, and also prevents
the intrusion of other creatures that live in the wood.
Then, too, v/hen the surrounding wood decays, or is eaten
av;ay by other animals, so as to endanger the life of the
"Ship-v.'orm" , the tube may be so strengthened as to serve
as the sole means of external protection. In this way the
walls of tubes which, protected, are usually not over a
qviarter to a half millimeter thick, may become two milli-
meters or more thick. This response of the animal to
changed conditions on the outside is a very mysterious one

19

and it is difficult to see by what means it recognizes its
danger.

The peculiar mode of life of Teredo has led to the
development of the palettes (firr. 20). These are protec-
tive strxictures peculiar to the "Ship-worms". They differ
somewhat in the various specios, but are essentiallj' cal-
careous paddles, attached one on either side of the poste-
rior end of the body. In Xylotrya the paddle part con-
sists of a series of funnel-shaped calcareous structures,
set one within the other ixpon a cylindrical handle, while
in Teredo it is composed of a single piece. The handle
of the paddle is imbedded in an invagination of the mantle
and the paddles project freely behind, whore by means of a
set of muscles, they may be protracted forcibly so as to
completely close the outer end of the burrow, aj^ainst the
intrusion of any enemy from the outside. AIgo, when the
burrow extends upwards and is more or less exposed at low
side, the palettes may so hermetically close the external
opening as to retain the water in the b' :';-ow, and to pre-
vent the collapse of the body of the "Ship-worms". 'i'-.e
action of the pfflettes is sliown in fi/^Ui'es 21 and .::.. V/hen

20

the animul is foeding, the palottos ■■ >-" 'Ir-^vrr for.vards ar.d
tlie siphons are extended freely into the wat shown

'g. 21. YAien it is disturbed ii. , ■^'^ siphons
are contracted very tmickly and the palettes forced into
the end of the tube us shov/n

Mode of Btirro-.ving. - The manner of mechanical forpiation of
the burrow has been one of the most debated questions in
the natural history of the "^-Jiip-worms" and their allies.
In Teredo, various structures have had. this work assigned
to them, by various observers. In some cases tlie observ-
ers thought some chemical solvent to assist the mechanical
action by softening the wood. Hancock thought there were
siliceous particles in the mantle, to do the v/ork. He
probably observed the teeth as yet unattached to the shell.
Quatrefages thought it the "cephalic hood", aided by some
chemical solvent. This structure he described cs muscular,
though it is but little muscular and could do no such im-
portant work as he assigned to it. Jeffreys thought it
the foot, which by other observers v/as described as wholly
absent. Osier, in 1826, had suspected the real mode of
formation, though he did not actually observe it. The

21

The sholl is the af;eut , assisted by the foot, as I liave
actually observed in young specimens under the microscope.
The whole structure of the shell and the arrancenent of
its adductor muscles indicate this mode. The teeth on the
anterior edges of the valves point outwards and backwards.
On both dorsal and ventral portions of each valve (figs.
IS and 19) there are stout calcareous knobs, which form a
double pivot by which the valves swing upon each other, by
the contraction of the adductor muscles. The mode of bur-
rowing is as follows: Wliile the foot performs a cupping
action, so as to draw the shell close against the surface
of the wood, the posterior adductor muscle contracts, so
that the teeth on the shell rasp away the v/ood. The valves
are brought to the original position by the small adductor.
The comparatively very large posterior adductor is there-
fore the active a^ent that does the work, aided by the
foot; the shell is the tool by which it is done.

Ingestion of Wood and Food.- As in other Lamellibranchs ,
a constant stream of water is passing through the siphons
when they are extended into the water, which serves for
respiration and also contains the small organisms which

22

sei've for food. Those consist mainly of diatoms and
simple floating Algae, and other minute organisms. Small
Crustacea and other animal forms seom almost nevor oaten.
The particles of v/ood that are rasped away in form-
ing the burrow are ingested, as the only r.vjjans o:' trotting
rid of them. It has often been debated v^hether they xin-
dergo any digestion in the alimentary canal, and I am in-
clined to think they contribute something to the nutrition
of "Siiip-wonns". Boring I tliink to be a periodical func-
tion, perhaps alternating with more active ingestion of
food. This is indicated by two facts. In the first place
it seems that while the teeth are boing cemented to the
anterior edges of the valves , the shell coi-ld not be used.
Also, the caecum of the stomach contains mainly particles
of v/ood, v/hich indicates that v/hile burrowing, the orifice
into it is open. The caecum contains a very large fold of
the internal membrane tfif^s. 31-33) and seems so eminently
an absorbent structure, that for this reason it seems to
me there must be some action on the particles of wood '.vith-
in it.

23

IV. ORr,y\J:IZATION AND LATE DEVELOPMENT OF THE "SHIP-V/ORMS.
a. The Gonoral O;-/: '...i;-.at ion.

In their form and general oi'f:;anization, the adult
".'^'hip-worms" aro the most peculiar and striking of all the
Lamcllibranchs. Their newly-attached larvae have the form
and most of the organization of the larvae typical of most
of the ir.urine Lamellibranchs , v/hich are free-sv^imming dur-
ing their larval development. The transfomiation of the
typical larva into the highly specialized "Sh.ip-v/^orm"
takes place v;ith such great rapidity as to properly be
called a metamorphosis.

The Larva and its i.ieta: cwphosis. - The general shape
of tlae newly-attachod larva (fig. 1) is that of a small
clam, v^itli equal shell valves. These latter are broader
than long, so that this Lamellibranch which has a more
elongated adult, has a larva more fore-shortened perhaps ,
than any other form. The yoixngest specimens I have foixnd
were creeping over tlie surface of the wood by means of
their very active, tongue-shaped foot. The velum v.-as in
all cases retract^^d into the large velar cavity (v.c), a
large space in the anterior, dorsal part of the shell cav-
ity, v.vn in fig. 24, v/hich is a sagittal section

24

of a nev;ly-attached larva. T'-" 'mo' . ''at
this stage io very long, ciliated over most ol' ite extent,
and angular at its jioGtorior end. Tl;is angular portion is
occupied by a well developed, tlxough simple byssus appara-
tus, whicli throws out a single, simple byssus thread, sev-
eral times as long as th.o diameter of the larva. This
serves to secure th.e 1m -va in the early stages of attach-
ment, so that, after the veliim has been lost, it may still
return to its mooring if it lose its footing from any
cause.

The siphons are already \foll developed in the larva,
the ventral (i.s. figs. 1,?.,24) with ciliated sensory pa-
pillae, the dorSal (e.S.), a simple non-ciliated tube. The
gills have advanced but liotle beyond the stage figured by
h'atschek (5) for the viviparous larva studied by him. On
each side of the body there are two large gill-slits, ■■-.
in the gill membrane, the rudiment of a third. Tho
worm" larva is a typical dimyarian. Both adductor nuscles
are present in their usual positions, the posterior (fig.
24, a. p.) already larger than the anterior (:\.y.). The
I'ctractors of the foot at this stage are attached in the
unbonal region of the shell just in front of the poste-

25

I'ior adductor.

The ulimentary canal is ali'eady hi,";hly specialized
'■''"'■'s. 1,24). A comi)aratively lonf;; oesophar^is < <- . o . )
loads into the stomach, from which a sinrjle lar o livor
vesicle projects on either side. The sheath j. ..iiO crys-
talline style projects from the posterior ventral portion
of the stomach on the midline. The intestine leaves tlie
stomach from the rif^ht side, anteriorly, and the caeci.im
peculiar to the Pholadacea is present as a hemispherical
rudiment on the right side, just postei-ior to the opening
of the intestine.

The nervous system of the larva (figs'. 2,59) is
hi.f^ly specialized. The f5anglia are comi-osed of ganglion
cells and the connectives contain only nerve-fibres. On
eitiier side the pleural (pi) ganglion is still separate
from the cerebral (c). From the pleural a connective pas-
ses to the visceral, ana from the cerebral, one to the
pedal. 1 think a pleura-pedal connective is also present,
but this I am not aule to state positively. The two pe-
dal ganglia are closoly fused, v.-liile the visceral are wide
apart.

The kidneys (k. fir-. 2) consist of large vacuolated

26

cells, end open oxtomally in fi'ont '•"f 1 ' '■« 'posterior ad-
ductor. The internal, pericardial openings I have not
been able to find. Lyinf; around the cerebral ^'••""' -lion is
a gland, wliich so far as known, is peculiar to " ip-
womis" and whicli in later stages, becomes so rroatly de-
veloped in connection with the gills. The glandular por-
tion (c;.!). , rig.2u) contains spherical cells, and from it
a duct opens to the exterior (d.D. ) under the cerebral
r:anrlion.

»Metamorphosis. - The duration of the f ree-swimrning life
of th.olarva is not knovm, but it is perhaps a month, more
or Itss. In a very much shorter period, the peculiar
"Siiip-v/orm" has been developed, with adult organization.
The first change is the sudden, com];)lete loss of the velum.
V/ithin a few hours after the larva has settled, tlie veliom
begins to disintegrate, and its constituent cells are cast
off and eated by the larva. The lower lip is projected
forv/ards under the cavity of the veliun, and as the cells
are cast off, they cannot pass to the exterior, and
eaten. The basement membrane of the cells of the velum
contracts rapidly and the cavity of the velum is very

27

quickly obliterated (within a few hours).

Accompanying the loss of the velum, the lonf^ byssus
thi'ead has been secreted. As soon as the lai'va ia secure,
it seeks a place to burrow, and in pr'-jparation for its fu-
ture life, its whole organization be{];ins to chanf^e. The
fusion of the mantle ventrally prorrtsses rapidly, and
within tv/o or tliree days (fig;. 3) only the opening for the
foot is left. The siphons elongate rapidly and very early,
the mantle grovrs out so as to project beyond the shell.
The latter changes rapidly after a ttaclirnent . V/ithin two
days the first row of teeth has been formed on either
valve; the greater grov^th on the ventral edges causes the
t'.vo valves to gape for the protrvision of the foot; tlie
knobs have been formed on dorsal and ventral portions; the
apophyses have been formed and the i-otractor muscles of the
foot have become attached to them. The foot, meanwhile, has
become pestle-shaped.

The alimontai-y canal takes an important part in the
general change. The caecum of the stomach, present in the
larva as a rudiment, enlarges very rapidly, and even be-
fore woody material has been ingested in quantity, it pro-
jects I.- a large vesicle into the foot. In the early
sty"- - f-.' . (4 days attached, a half millimeter

2R

long;) it already rorins a lai-f^j yv.it. ^^ . ■vi..ceral pimgs.
As tho ingestion of woody materials progresses, the caeciim
projocts more and more postoriorly, and in specimens 2 mm.
long (fir;*'''), it extends ntuch beyond the posterior adduc-
tor. Tho gills soon grow aroi.md the i'oot posteriorly and
in specimens 2 mm. long, ten to tv;elve days old, project
much beyond the visceral mass (fig. 7), This same stage
also shows the pericardial space, v;ith its contained and
associated structures, in the position v/hich it occupies
in the adult, distinctlj'' posterior to the large adductor.
And, in this, as in subsequent stages the visceral gan-
glion lies on the posterior end of the pericardial cavity.

There ai-e a number of facts in the organization and
metamorphosis of the larva that seem to have a wider sig-
nificance. One of these is the sudden and complete loss
of the velum. Lovin thought that, in forms studied by
him,, it entered into the formation of the labial palps.
These structures are present in X. fimbriata only as the
small ridges on the sides of a sliglit groove around the
mouth; so that a form in which they may be said to bo ab-
sent, does not give necessary evidence against the deriva-
tion of tlie palps from the velum in forms in v/hich the

29

formoi* are woll dcvelopGd. However, the velijin in various
Lame 1 lib ranch larvae is very much larn:er than the palps in
early stages, so that most of it must be cast oil' or ab-
sorbed. In the newly-attached oyster I have observed that
the cells of the velum are absorbed more clowly, though /
the palps are developed somewhat later mo.-ely as ridges on
the sides of the mouth. The evidence from X. fimbriata
and 0. virr-iniana, it seems to me, shows conclusively that
the palps arc not derived from the velum. The loss of the

velum is an event not confined to the Lamellibranchs. Wil-

(17)
son has observed that the trochal cells of Polygordius

are suddenly cast off and eaten as in X. fimbriata, and

Pruvot has described the loss of the test in nondessia.

These all seem to be one and the same phenomenon, and indi^

cate that the loss of a part of the ectodermal covering in

these and many other forms is a very primitive and general

occurrence.

The addition of the "S;^.ip-worms"to the forms which
have heretofore been knovm to possess a byssus apparatus,
indicates that this structure is pey... iversal in La-
mellibranch larvae, though in the adult it may become de-
generate. I may add that 1" ni-tr"-' •"i • -i'^* n-vi .'^ byssus

iU

apparatvis is present in the newly- attached larvae, though
here a secretion is thrown out for the attachment of the
left valve, and does not form a byssus tliread. In forms
like Teredo and Ostrea tlie byssus serves for the attach-
ment of the young bivalves, and apparently it has the same
purpose in othei- forms in v/hich it is present in t!-.e young
(Pecten) , but is lost in the adult. In Sphaeriiim it serves
to attach the viviparous larva to the wall of the brood
chamber. All the known facts go to show that the byssus-
apparatus has been developed to assist in the transforma-
tion of the free-swimming palagic larva into the bivalve
viith an attached or other settled mode of life; and that,
the transformation having taken place, the bysus may be
lost;or may be retained in forms which are permanently at-
tached, but lack other means than the byssus for attach-
ment.

The sheath of the crystalline style is well develop-
ed in the newly-attached larva. However, everything in-
dicated its fonmtion from the posterior end of the stom-
ach. If we imagine the intestine leaving the blind end
of the sheath, we get a fom very like Nucula and Yoldia,
in which the posterior half of the stomach has the same

31

structure and function as the slieath in other forms .tliough
no style is formed. As the intestine has loft its median
position at the extreme posterior end of the stomach in
the development of more specialized forms, it has reraained
attached to various parts of the sheath of the style, as
in Oardium, and has reached its greatest displacement in
forms like Teredo and Pholas, in v/hich it leaves the stom-
ach from one side, and in which the sheath of the style
forms a large blind pouch. If this view of the relations
of the stomach, intestine, and sheath be the correct one,
then the slieath is not a structure which has been acquired
in the more highly specialized forms. It is homologous
with the posterior part of the stomach of primitive forms
like !Tucula and Yoldia, while the intestine has left its
original madian attacliment to the posterior end, to be at-
tached to one side of, the stomach.

b. The General Organization of the Adult.

After the preceding description of the Ip.rva and its
metamorphosis, the general plan of the adult ".,i.ip-v/orm"

32

v/ill be easily understood. i Tor X/l'.-

ti-ya in x'l/rc. 8-10. Fi .

>s long as it is taken J'rom its tube, from the
loft . At tlie anterior end, on the left, th^ "head"
is covered by the small shell, over whose dorsal and poste-
rior portions iluplicatures of the mantle project. Behind
the shell, - long, naked body extends, tapering so that
the whole '".Vorm" forms a truncated cone. At the posterior-
end are si'.ovm the points of attachment to the calcareous
tube; and from it project the pallottes and siphons. From
the anterior end, between the gaping shell valves, pro-
jects the pestle-shaped foot.

The nalced, projecting part of the body is tlie man-
tle. If it is removed (:'i:. 0) the long gills are ox -
posed posteriorly and the large visceral mass anteriorly.
The latter is continuous witli the foot and extends about
tv/o-fifths of the length of th.e body. It contains the
viscera (alimentary canal, genital organs, etc.). Dorsal
to it (fir;. 10) lies the large pericardial cavity v.-ith its
contained and associated sti'uctures (heart, kidneys, vis-
ceral ganglion). Dorsal to the pericardial cavity is the
long, narrow anal canal, into which the rectum opens above

the postoi'ior adductor muscle, una wuici; il; cintinuous
witli the epibranchial cavity behind the visceral ranfrlion.
i::u u:.''!! ciivitj' is occiipied mostly by the loot , aiici :;y
the two adductor muscles wliich are common to most Lamel-
libranchs.

7A

c. The Shell and Palettes.

The Shell.- The nov/ly-attachcd "Ship-worm" larva por.:;os-
ses a typical bivalve shell. The valves are equal and uni-
ted dorsally by a well-developed hinge apparatus. The
shell in side view is v/ider than long; the transversal
diameter is about equal to the longitudinal. The ri.^ht
valve (fig. 11) bears three equal hinge teeth; the left,
two. Dorsal to the teeth is an external hinge ligament.
In either valve, the apophyses of l-ater stages is present
as a rudiment. Up to this time grov/'th has taken place
along concentric lines. From this time on, rapid, very
iinequal growth in different parts of the valves causes a
sudden transforniiat ion of the shell, which becomes very
different from that of the typical bivalve. The initial
stages in this change are shown in fig. 14, v^hich is an
anterior view of the shell of a "Ship-worm" which has been
in the '.vood a day or less. After growing a small amoixnt ,
the anterior border has cemented to it a row of teeth
which have been secreted separately in small pockets in
the epithelium of the anterior edge of the mantle. The
first row of teeth, as well as those formed through life.

point outwards and backwards. The apophysis, present as
a small rvidinient in the larval shell, has r^ro'Vfn out into
the shell cavity, pushing the mantle invagination before
it; and in this very rapidly attained stage, is almost as
large ccmparatively as in the adult. Meanwhile, tlie ven-
tral edge of the valve has grown rapidly, and there have
appeared on the dorsal and ventral portions th.e two knobs,
upon v/hich the two valves swing in this and subsequent
stages, during the mechanical process of boring. During
these changes, the hinge teeth have disappeared, probably
by absorption. The valves which, during larval life, have
svmng at the hinge so as to open or close the shell cavity
on the ventral side, come to swing u]ion the knobs along
a median transverse axis vertical to the axis of the
hinge. The greater growth of the valves on their ventral
edges causes them to gape before and beliind for the pro-
trusion of the foot and siphons.

Growth of the valves continues with great rapidity.
The left valve of a specimen 1 mm. long is shown in oblique
view in fig. 15. The chief features that have been intro-
duced are as follows: The point of greatest growth is on
the vontral edge. The line of growth, and hence the rows

of teeth, are wider apart on the dorsal half oi' tlie ante-
rior border than on the ventral. In this way, an anfi;le
is fcirmed, v/hich soon (fig. IG) becomes a ri.";ht anp;le.
Meanwhile, the posterior border has grown rapidly and
flares outwards so as to give better purchase for the pos-
terior adductor during its contraction. Likev/ise, a much
smaller portion of the dorsal anterior edge flares out-
wards for the attacliment of the anterior adductor (fig. 18).

There is little modification in form or structure of
the shell after the stage siiown in fig. 16, v/liich is a
side-viev: of theleft valve from a specimen 5 mm. long. As
groY/th on the ventral edge takes place, the knob is con-
stantly being added to towards the midline and absorbed on
the side tov/ards the concavity of the valve. And as j^rov/th
at the posterior border takes place, the posterior adduc-
tor is constantly moving backwards. In the larval and
subsequent stages, the whole shell, including the teeth,
is covered externally by an epidermis.

The Palettes,- These stinictures are peculiar to the
"Ship-v/orms" and have been acquired for the purpose of
closing the outer ends of the burrow against intruders.
The structure of one of these is shown in fig. 20, which

37

repi'esents the left palette of a specimen 5 mm. lonf^. It
consists of a series of seven funnel-shaped structures
wliich have been foi'med and cemented in succession to the
handle. The formation of the palettes is as follows :-
In specimens still less than 1 mm, long, the mantle of the
posterior region has foi-med a duplicature (figs. 4,7)which
project over the base of the siphons. At the anterior
portions of the sides of the space tlius formed, the epith-
elium of either side pushes forwards. In tlie invagina-
tion thus formed, the handle of the palette is formed, and
projects into the "collar" space. The lining walls of the
sides of the co'llar space secrete the funnel-shaped ])ieces
which are cemented to the handle. New larger pieces are
added at the anterior end, and those first formed may be
broken off. In Teredo, the paddle part of the palette is
a solid piece and not divided into pieces, as has just
been described for Xylotrya. Strictly speaking, the seg-
ments of a palette are semi-circular when seen on end.
lYhen the two palettes are brought together in closing the
tube, they form a truncated cone.

38

d. The Mantle and Siphons,

In the adult "Ship-v.'orm" (fig. 3) the mantle forms a
verj- lonr, and veiv delicate tube, which stretches from the
anterior edge of the shell, to tlie ends of the siphons,
which are modifications of the mantle, as in other forms
of Lamellibranchs. This tube is open only at the anterior
end, the pedal opening for the protrusion of the foot; and
at the ends of the siphons, the inhalent and exhalent
openings. It was formerly a much debated question, how
mxich of this tube should be considered body proper, and
hovr much siphons. In the lif^t of our present knowledge,
it is easy to see that the muscular collar marks off the
end of tlie body and the beginning of the siphons.

The mantle of Teredo has undergone more differenti-
ation than in any other Lamellibranch. The anterior edf;e
is thickened, as in other forms, and secretes the teeth,
the edges of the valves andthe epidoiTiis. The very deli-
cate part iHiderlying the shell and stretching to the si-
phons, secretes the inner layers of the shell, and the
calcareous tube lining the burrow. Witliin the slioll cav-
ity, induplicatures secrete the apophyses and at the sane
time absorb part of them as they change shape and position:

39

also other parts secrete the two rairs of knobs on the
valves. The posterior edr^e of the shell is not marked by
the tliickened mantle ea^e at; in otiier types, but lorms a
duplicature around the v/hole posterior edge of the shell,
which stretches for^^fards. In the dorsal ret^ion, the whole
umbonal region of the valves is covered by this duplica-
ture and tO- this special part, Quatrefages gave the name
of "cephalic-hood". (£.h. figs. 7,28). To it he assigned
the fvmction of fomning the burrow. It is somewhat, but
not very muscular, and no such important work could be
done by it. In the collar region it has been seen that
the mantle forms Lho duplicature or collar which projects
posteriorly over the base of the siphons; and within the
cavity of which the handles and paddles of the palettes
are formed separately (figs. 7,10). The siphons as part of
the mantle, form tvro long tubes (figs. 7-9) which are fus-
ed together through half or more of their extent. The
anal or exhalent siphon is wit;:out papillae or tentacles
and is shorter and less muscular than the respiratory or
inlialent siphon, which bears a number of tentacles (figs.
7-9), These are sensory structures, which also serve to
close the entrance of the respiratory siphon very quick-
ly.

40

Betweon the diiplicature at tlio posterior '.'a^;G of the
shell and of the collar, the mantle is very uniform. Its
structure io as follows:- Externally, the surface epith-
elium is composed of the flattened, non-ciliatod cells,
which secrete the calcareous lining of tiie burrow. Inter-
nal to the outer epithelium, are the weak m^iscles of the
mantle, consisting of the longitudinal layer; a layer in
which, the fibres cross obliquely to the longitudinal bi-
bres; and internal to these, the circular layer. The in-
ternal surface of the mantle (the lining of the mantle
cavity) , is lined by cells T;hich in general are columnar
and ciliated. Opposite the ends of the gills, the mantle
is strongly ciliated and bears numerous mucous gland cells
which empty to the surface. This region is indicated di-
agrammatically in figs. 29-34 » where on either side v.-en-
tral to the ciliated, glandular area the mantle vrall is
th.ickened, so as to form a groove opposite the groove of
the gill.

Betv/een the two epithelial layers of the mantle,
there is a reticular not-v;ork formed of connective tis-
sue, -.vith a siiiall amount of muscle and nerve fibres, etc.
The spaces so formed are lacunar blood spaces which are

41

filled by a peculiar substance wliOLje nature I liave not
been able to determine. In living specimens tlie mantle is
of a light grayish, translucent appearance. But specimens
in alcohol become of almost a chalky whiteness, due to tha
masses of this peculiar material. Each lacunar space is
filled by a more or less spherical nodule, which is just
visible to the naked eye. Examined by transmitted light,
these nodules are very opaque and seem composed of granu-
lar particles; by reflected light they are white. They
are insoluble in acids, but soluble in water and quickly
disappear in aqueous solutions. Deshayes described them
as non-nucleated mucous cells. They are apparently the
"siliceous particles" which Hancock observed, and with
which he supposed the burrow to be formed. They are not
cells, but deposits of some sort. It seems that they
ahould be regarded as constituting a reserve of mucilagi-
nous material of some sort for use as occasion may require.

Special Gland of tlie Mantle. - Lying between the two ep-
idermal layers of the mantle, in the mid-dorsal region
near the extreme posterior end of the body, there is a
small special gland which is peculiar to the "Ship-wormn !• .

42

Its position is shown in fics. C a.u 'J ; ana its extent and
structure in fig. 22, which repi-esents a transvorse sec-
tion of the whole f^land in a specimen about a half centi-
meter long. The gland consists of numerous^ more or less
spherical, vesicular acini whose average diameter is about
a fortieth millimeter. They are lined by flattened, non-
ciliated, slightly granular cells. From the gland a duct
passes posteriorly to open on the dorsal outer surface.

This gland appears in the young "Ship-worm" soon af-
ter attachment as a single median small vesicle, of appa-
rently epidermal derivation. As the animal grows , new ves-
icles are formed as outgrov/^ths from those already present.
What the function of the gland is, iias not been determined,
but its position indicates that it may be the secretion of
a poison noxious to enemies that may get into the end of
the "Ship-v^orm" bui'row.

e. The Muscular System.

Early in this century it was one oJ' the mont debat-
ed questions in Zoology, whether the imiscle then known in
the "Ship-v/orms" was liomoloj-ous witli the anterior or pos-

43

terior adductor oi' other Laniollibranchs , or witii both com-
bined. It was Grobben who established the homology of the
muscles w'len he discovered (5) the two small anterior ad-
ductor, which had been overlooked before.

In the general transformation of the larva into the
"Ship-worm", the ligament, which in the larva opposes the
tv/o adductor muscles comes to serve only to keep the two
valves from separating from each other. And the two mus-
cles, which in the larva oppose the action of the liga-
ment, to close the sliell,come to cause the two valves to
svfing upon each other on the dorsal and ventral knobs of
the shell valves, during the process of boring. So the
tvio adductors become antagonistic to each other.

In the newly-attached laiva, both adductors are pres-
ent, the posterior (a.jo. figs. 2,24) already considerably
larger than the anterior (a. a) . Both are attached in the
concavity of the shell valve and well towards the dorsal
side. In the general transformation, the adductor muscles
as the active mechanical agents in boring, undergo consid-
erable change. The posterior, as the one that really does
the work, becomes very large (figs. 7,9,10), and passes pos-
teriorly to be attached to the outwardly turned edges of

44

the sliell (figs. 15-17) so as to civ-^ it u ttL-r purchase
during its contraction. Tho antaripr, whosn only work is
to bring tiio shell valves back to tlieir original position,
after contraction of the posterior, is comparatively very
small (figs, 7,9,10, a_.a. ) , and moves forvrards from the
position in the larva, to be attached to the anterior,
outwardly turned edges of the shell valves.

In minute structure , all of the muscle fibres of
both adductors are apparently striated, due to a more or
less regular deposit of granular material on their surface.
This structure seems to su.pport the viev/- held of the tv/o
parts of the addiictor in forms like Pecton. One part is
tendinous and is supposed to prevent the shell valves from
separating too far. The otlier part is for active adduc-
tion of the valves. In Teredo, where it is not necessary
to oppose the action of a hinge ligament, all parts of
both muscles are of the same character as that part in
Pecten w'nich is supposed to serve for active adduction.

The pedal muscles in the larva are tb.ose typical of
Lamellibranchs with a foot. A pair of protractors of the
foot are attached in the anterior umbonal region of the
shell valves; and a pair of retractors, in the posterior

45

umbonal region, anterior to the attacament oi tlie ijoste-
rior adductor {.v_.ji.Q_. fiR. 26). Witli the remarkable ap-
peai-ance of tlie apophyses or tlie shell, the pedal muscles
suddenly lose their old attachment in the umbonal region,
to become attached to the apophyses through almost the
whole length of the latter. After this shifting, which
talces place as the young "Ship-worm" begins to bore, the
padal muscles no longer form distinct muscles, but wide
bands which run from the apophyses to be distributed
aroiind the sides of the foot.

In Teredo, the posterior end of the body, which has
usually been described as the "muscular collar", contains
a number of highly specialized muscles, some of which are
peculiar to the "Ship-wonns", Their general arrangement,
and their relations to the palettes and calcareous tube
ai-e si.o^vn in figs. 21 and 22. They are divided into two
sets, those which manipulate the palettes, and those which
are distributed to the siphons. The first set consists of
a pair of protractors of the palettes (£.j2. ) , two pairs
of retractors of the palettes (r.£. ) and a sin.";le adductor
pf the palettes (a_.£. ) . On either side the protractor of
the palette in in^orted along the hand! n of tlie palette.

46

whence it radiates to be attached to the side of the cal-
careous tube along a broad line, its orip;in. On cither
side tliere are two retractors of the palette. One is in-
serted on the end of the handle and passes forwards to be
distributed in the mantle' along the sides of the body.
The other is inserted near the outer end of the handle,
whence it runs forwards to be attached alone with the si-
phonal muscles. The adductor is a stout, cylindrical mus-
cle, stretching between the anterior ends of the palette
handles, and lyinr; in the septum which divides the mantle
cavity posteriorly. The muscles of the siphons are at-
tached on either side along a triangular area to txie cal-
careous tube, sliglitly anterior and ventral to the attach-
ment of the palette muscles. From tiiis origin the siphon-
al muscles arc distributed to the siphons , mostly to the
respiratory.

The action of the muscles of the palettes and si-
phons is as foll07/s:- When the "Ship- worm" is undicturbe4
the siphons are widely extended, as represented in fig. 21.
If disturbed in any vmy , the siphons are retracted with
great rapidity by the contraction of their muscles. At
the same time, by the action of the pi'Otractors of the

47

palettes, the palettes are pushed forcibly into the end of
the tube so as to completely close the latter. The outer
ends of the paddles are brought together by the sides of
the tube, while the anterior ends of the handles are sep-
arated. As the disturbance disappears, the palettes seem
dislodged by the ventral retractors, and retraction seems
to be completed by the long muscles attached to the ends
of the handles. At the same time, by the action of the
adductor of the palettes, their paddles are separated, so
as to permit the extension of the siphons by an inflov/ of
blood.

From this description, it is seen that the end of
the tube of Teredo is homologous with tlie pallial sinus
of typical Lamellibranchs. The same siphonal muscles are
present as in other forms, while the muscles of the pal-
ettes are peculiar to the "Ship-worms".

48

f. The Respiratory System.

The gills of Teredo are perhaps more highly special-
ized than those of any otiier type of Lainellibranch. For,
besides possessing a membranous, non-perforato portion
which reminds one of the gill structure in the Septibran-
chia, they are otherv^ise sharply marked off from those of
forms nearly related to the "ghip-worms".

The Development and General Structure of the Gills.- The
embryonic development of the gills of Teredo has been ob-
served by Hatschek (6) in the viviparous larva of the un-
identified species studied by him. Here the rudimentary
gill of either side is a fold, in vrhich perforations ap-
pear in succession, new ones being added postei'ior to
those already formed. In the newly-attached larva, the
gills have advanced but little beyond the stage described
by Hatschek. On either side there are two slits and the
rudiment of a third. However, the slits have so increased
in size as to occupy most of the space on the upper sides
of the foot, and the gill-fold has fused to the sides of
the foot by its ventral edge. In this way, the triii-snts

49

come to separate barij or lilainonts attaciied ut both ends
(fig. 2G). And aa the fold, when it appears, is attached
at the point of insertion of the mantle on the sides of
the body, and the ventral edfje fuses v/ith the upper part
of the foot the gill-bars or filaments lie almost hori-
zontally in the mantle chamber.

This mode of formation of gill-slits in a fold which
±\ises continuously, at first with the sides of the body
and visceral mass (fig. 3) and later, v/ith its fellow of
the opposite side as well (fig. 6) is kept up during lil'e.
However, beginning with stages still loss than 1 mm. long,
the process is modified as follo'.vs:- In specimens less
than 1 mm. long (fig. 3) the gill of either side consists
of a membrane with a series of gill slits which decrease
in size from before backwards. When, however, there are
about fifteen slits in the series, a perforation in tlie
gill-fold or membrane appears opposite and internal to the
tenth (usually, rarely ninth or eleventh) slit of the
first series. Mew ones are added in succession posterior
to it, so that a second series of slits comes to be formed

internal to the first (fig. 6). At the posterior end the

la^-s
intern'-il always slightly behind the extei-nal in its devel-
opment. As shown in I'ig. 6, there are no slits in the in-

50

ternal scries internal to the ten first formed in the ex-
ternal, and none ever appear.

The f^ill-fold and ciH ^^ the young Teredo represent
the internal half of the I.'olluscan ctenidium. From tlie
resemblance of the mode of development to tliat in Cyclas
(Ziegler) and *'ytilus (Lacaze-Duthiers ) , it is seen that
the slits of the first formed series separate the descend-
ing limbs of the Lame lli'o ranch ^:ill filaments; and that
the second series separate the ascending limbs. The ante-
rior* ten filaments, then, never develop the ascending
limbs. Likewise, the other half of the ctenidium is never
developed in Teredo, contrary to the belief of Deshayes
and Quatref ages , ViTho believed the whole ctenidium, or
"pair" of gills to be present on either side of the body.

The term "gill-fold" I have used to designate the
posterior end or growing point of the gill, and "gill-fil-
aments", the elements that are formed from it. However,
in later stages, soon after that shown in fig. 3, the gi*ow-
ing point forms a more or less cylindrical hollow tube
filled by a blood space, v/hich fuses continuously on the
midline with its fellow of the opposite side, and dorsally
over a v/ide area (between th.e tv/o points indicated fus
in fig. 37) viith the mantle. In thir, vrny the ot ilrrnnrhial

51

cavity is sepax'ated from the rest or the mantle cavity.
Meanwhile, the free portion oj' th.e j-irowing point has be-
come angular, and at tlie sides of the angle the two series
of perforations are fomied progressively (fig,6), the ex-
ternal alvmys slightly in advance of the internal. The
corros]'onding slits of the tv/o series push in (in the di-
rection of the lower arrows in fig. 37) till they meet
each other and till they push through to the epibranchial
cavity. These inpushings divide the original blood space
of the grov/ing point into narrow spaces separated from
each other except at two points .the openings into the af-
ferent and efferent branchial veins. The median portion
of the original blood space remains undivided as the affer-
ent vein, and by the disappearance of the middle part of
the walls of the tv;o growing points as tliey fuse together,
the afferent veins of the two sides imite to form the
large afferent branchial vein. The undivided dorsal por-
tion persists as the efferent branchial vein on either
side. The walls of adjacent slits are coniiected together
by nunnerous connective-tissue cells (fig. 33) , so as to
form the gill lar.iinacj , the name given to them by Quatre-
fegejs , and more appropriate for the gill elei.icnts in Teredo

52

which (except the anterior ten) do not fonn I'ilaments.
From tlie mode of formation it is seen that there is a
large flat blood space in each la'nina, and that there is
a free flow of blood through the lamina (in the direction
of the arrows fig. 37) between the afferent and efferent
branchial veins.

In a yovmg Teredo a half centimeter in length (some-
v/hat later thai: ..^ stage represented in Pir^, G), there is
on either side a continuous series of seventy-five or more
gill filaments (filaments and laminae), stretching from
the mouth region, around the sides of the body, and pos-
terior to the visceral mass. Soon afterwards the "fila-
ment" between the tenth and eleventh (usually) gill-slits
broadens from before back'.vards. This grovrth increases
till, in the adult, the anterior ten filaments (it may
rarely be nine or eleven) are separated from the rest of
the gill by ten cm. or more, in large specimens. However,
they retain the structure and, doubtless, the function of
gill elements, though in the adult, they form a series of
plications on the sides of the "head" (fig.9).

In Teredo, the epibranchial cavity forms a long ca-
nal posteriorly (figs. 10,33,34 J but is divided anterior-

53

ly where the gills oJ" the two sides diverge from each oth-
er. As the ^anterior ten Tilatnents become separated i'rom
the rest of the gill, the epibranchial cavity remains as a
long, very narrow canal (op, ca. figs. 28-31) which lies
in '.he mantle on either side external to the afferent
branchial vein, and adjacent to tlie groove described be-
low.

The tv/o limbs of a gill lamina (fig. 37) form almost
a ri':;ht anrle v;ith each other. At the angle thore is a
ciliated groove (figs. 32,34, 37) v/hich expands the full
length of the gill in young specimens (fig. 6), and in ad-
ults, in addition, connects the anterior ten filaments
v/ith the rest of the gill (figs. 9,28-31). In the adult,
the connecting part of the groove, then, is really a part
of the gill and is homologous with the groove of one fil-
ament in other parts of the gill. The minute structure of
the groove is as follows:- Tlie lining cells are in the
main strongly ciliated and colvimnar (fig. 44) , but there are
distributed among them nvimerous mucous gland cells. The
internal surface of the mantle opposite the edge of the
gill, also forms a groove lined by strongly ciliated cells
with gland cells among them, and this with the groove of
the gill forms a sort of tube which conveys food to the

54

mouth.

The Minute Structure of the Gills. - It has been
seen that, by their mode of formation, the "intra-f ilamen-
tar imion" between the tv/o limbs of a lamina is so com-
plete, that blood may flow freely through the lamina from
the afferent to the efferent branchial vein. The"inter-
filamentar" connection, between adjacent laminae is also
very complete, but serves only for support and not for the
full interchange of blood. The general plan of the inter-
laminar connections is shown in fig. 39, which is a tan-
gential section of a gill alnost in the line of the let-
ters iX»J.* i^ fig* 38. It is seen that the points of union
in adjacent laminae are arranged in regular rows. At each
point, the supporting rod (s.r. fig, 40) projects through a
perforation, so as to bind together adjacent laminae. At-
tached to adjacent rods are fiber-like cells which are ap-
parently muscular, and contractile.

The minute stinxcture of the edges of a lamina is
similar to that of the filaments in forms like Mytilus,
though the various types of cells are more sharply marked
off from each other. At eith'^r side there are two rows of

55

large "lateral cells" (I.e. fig, 40), bearing long dense
cilia. External to these are small non-ciliated f^land

cells, and at the angles, the small, flattened "latere -

0 a c ! :
frontal'' cells (l.f.c. fig. 40), with a single rov; of stiff

cilia. The outer edge of the lamina ia occupied by numer-
ous small "frontal-cells** (f. c. ) v/hich bear numerous, weak-
er cilia. The two broad sides of the lamina are composed
of very flat cells without cell outlines or regular ar-
rangement, and are connected together by niimerous connect-
ive tissue cells which penetrate the blood space of the
lamina (b.S. figs. 38,40). In their minute structure
(fig. 41) the anterior ton filaments arc essentially like
the rest of the gill, except that the "frontal cells" are
more numerous, and the middle ones bear no cilia. The
first filament is only a half filament, indicating that
the filaments are formed by perforations in a gill mem-
brane, and not by the latter precocious fusion of gill
filaments. The long epibranchial canal is sparsely cil-
iated, and it seems that the function of the anterior ten
filaments is to get rid of superfluous water in the ante-
rior end of the burrow.

56

Glands of Deshayes. - Closely associated with the ciUs
or the adult is a pair of very complicated structures
v/hicli, so far as known, are peculiar to Teredo , and
which constitute one of the most important features wliich
distinr:uish the "Ship-v;onns"from other types of Lamelli-
branchs. In honor of the observer who first described
them, I have called them the glands of Deshayes. Though
he pointed them out, they have never boen fully described
as to character, structure and relations.

Deshayes observed a peculiar structure in the umbo-
nal region oh either side of the shell cavity. Ke describ-
ed it as of glandular nature, and supposed its function to
be the secretion of a fluid to soften v/ood in the forma-
tion of the burrov/. - In the gill laminae he described pe-
culiar modifications of the tissues, which he supposed to
be mucous glands, and to serve for the nutrition of the
viviparous embryos of Teredo. He also described a third
structLire, as invading a part of the walls of the afferent
brancheial vein, and of unkno-^m function. These three
glands described by Deshayes are parts of one and the same
structure which is present, in different degree of devel-
opment, in all of tlie three species I have studied. In
all three the part in the gill is well developed. In T.

57

norvegica, the vunbonal part is so large as to occupy a
considei*able part of the lambonal region of the shell cav-
ity; in X. f imbriata it is small, and in T. navalis , appa-
rently rudimentary. In his studies of the pericardial
glands in Lamellibranchs , Grobben sought in Teredo for the
gland riescribed by Deshayes in the umbonal region, think-
ing it might represent a part of the pericardial gland of
other forms which possess this organ. He failed to find
it and supposed it to be absent. Hov/ever, though he ap-
parently had none of the forms with which I have worked,
I think it was doubtless present in his species.

In the larva th.is peculiar structure is present on

either side in front of the cerebral ganglion, though in a

form
much simplified (g.D. fig. 2). It is vesicular and fil-
led with spherical cells of apparently nucous nature. A
duct leads to the exterior, opening at the side of the
mouth, on the ventral side of the velum.

The structure of subsequent stages oi' the gland will
be best linderstood by first describing that part in the
gill. A glance at fig. 38 will show that the modified por-
tion contains elements of two very different types of
structure. Their distribution and relations are best
shown in fig. 37, which represents a lamina from the gill of

58

T. navalis. This fiprure also s>iows the distribution of
the pland in the branchial vein, and that this portion is
ol" the same nature as that lying in the lamina adjacont to
it. Still farther from the vein, is tlie second typo of
structure. Ramifying in all directions from the latter
are dendritic processes, which penetrate the epithelial
walls of the lamina. These ramified portions are the pri-
mary structures, and the other two are derived from them.
The structure of the dendritic portion is shown in figs.
47 ,48, which were drawn vrnder a magnification of 1900 di-
ameter. The processes seem devoid of any membrane. The
contents consist of very minute filamentous structures ar-
ranged lengthwise in the direction of the process. Lying
i-n the mass thus formed are nuclei v/hich vary in niamber
and position. The middle one in fig. 48 indicates that
they may change position, and that the whole structure
forms a sincytiiom. The enlarged portions of the processes
shovm in fig. 37, became surrounded by an epithelial cov-
ering, apparently derived from the lining cells of the
lamina. This stage is represented in figs. 46 and 47.
The minute filamentous structures have taken on a more ir-
regular arrangement, and lying within the mass; are spher-

59

ical colls oi" varying appearance. VHiile some (fig. 45)
are coarsely granular, others are almost homogenous. The
nuclei lie to one side of the cells.

The other type of structure (figs. 50-52) I am con-
fident tliough not perfectly sure, is also derived from the
dendritic processes, along with a modification of the sur-
rovmding epitheliiom. The developed structure is of re-
markable ai^pearance (fig. 52). The base is composed of
modified epitheli-um cells of the v/all of the lamina. The
nuclei stain liglitly and lie in a granular protoplasm,
from which deeply staining rods project into the blood -
space, but from which they are separated by a membrane
formed of very flat cells. The development of this stinac-
tvu'e seems to be as f ollov/s : When the dendritic proces-
ses penetrate among the epithelial cells (fig. 49) , the
filaments are arranged lengthwise; soon they take on a
vertical position (fig. 50) enlarge, and become covered by
the cap-like membrane (figs. 50-52). If this derivation
be tho correct one, then the rods in fig. 52 have been
formed by the enlargement of the filaments of tlie dendri-
tic structures. In the lamina the rods project into the
blood-space; in the afferent branchial vein, away from the

60

blood space. Wi\y tlie difference, I do not know.

The development of the gland of the adult, so far as
I cin detormine, is as follows:- Yrtien the snail Teredo
have been in the wood for a day or so, the gland of the
larva sends out processes which invade the surroiinding ec-
todermal tissues (the mantle, sides of the body). As the
side of the body becomes enlarged, it fuses with the dor-
sal sides of the gill filaments (fig. 27). From the first
there is close association between the gland and the gill.
As the latter grows, the filaments become invaded by the
gland; and as the anterior ten filaments become separated
from the rest of the gill, the two parts of the gland re-
main connected together by a long, narrow duct which ac-
companies the epibranchial canal and lies in the afferent
branchial vein (figs. 28-32). With the separation of the
tyro parts of the gill, the intervening part of the gland
disappears in X. fimbriata and T. navalis, but persists
in T. norvegica. As the gland enters the gill lamina, it
remains connected by a small duct with the main duct, and
sends the granular cells into tb.e latter. The main duct
may become gorged with granular cells (fig. 47). However,
in most cases there are few cells in it, and I am inclined

61

to regard it (at least in X. fimbriata) as defucnerate.
Likevfise, I am inclined to repjard the rormation of the
spherical cells, in the one part, as not the ctiief func-
tion of this part of the ^land. The origin and fate of
the cells I have not been able to determine. Their con-
tents suggest that they may be modified mucous gland
cells.

V/hat the special function of this remarkable struc-
ture is I am not able to even guess. The rudimentary
character of the anterior part in the "head" of T. nava-
lis indicates that it cannot be the formation of a secre-
tion to soften v/ood. Its development in the gill, in
small as v;ell as large individuals, in male and female,
and in forms that do not retain the eggs in the gills,
proves that this part caiinot be for the nutrition of viv-
iparous embryos. The close connection with the gill indi-
cates , it seems to me , that its function is probably the
elaboration of some internal secretion for whose formation
the presence of both blood and water is necessary.

62

g. The Circulatory System.

The circulatory system of the "Ship-v^orms" is pecu-
liar in relation to tlie peculiar form of the body. The
growth of the visceral mass ventrally at first, and after-
wards its {jreat elongation posterially along with the
elongation of the rest of the body accounts for the chan-
ges tliat have taken place. Doubtless the ancestors of Te-
redo were Lamellibranchs with typical circulation, in
which on either side in the pericardial cavity lay an aviricle
latent to, and emptying into, the median ventricle vrhich
surrounded the intestine. . From the ventricle the ante-
rior aorta passed forv/ard above the intestine and the pos-
terior aorta backward below the intestine. In Teredo,
the pericardial space, v/ith its contained parts, has come
to lie on the morphologically ventral side of the intes-
tine, and the relations of the various parts of the circu-
latory system to each other have been radically changed.

The youngest stage of the circulatory system I have
observed in detail is in specimens 2 rnm. long. Here the
heart consists of two almost separate halves (fig. 52). On
either side a more or less spherical auricle (an. ) lies
lateral and slightly vential to, and loads into, a more or

63

less spherical ventricle (ve.) Either ventricle sends a
very narrow, vessel-like portion towards the mid-line
where the two sides unite. In this middle portion there
are two semilunar valves (fig. 55) on the dorsal and ven-
tral sides, and from this point two vessels emerge. One
runs anteriorly, and bending around the posterior adductor
muscle, r\ins posteriorly in the mantle. At this star;e,
the visceral nmss lias projected but little posteriorly
(fig«6), and the second vessel from the heart, somewhat
smaller than the other, runs ventrally into the visceral
mass. These structures are shown in section in fig. 54,
which is a longitudinal section through the median part of
the ventricles and aortae in a specimen 4 mm. long.

In the stage in v;hich the heai-t is developing, the
stomach and caecum already occupy most of the visceral
mass, and the gills are wide apart. This may account for
the wide separation of the tvra halves of the heart. In
development posteriorly, the gills advance ahead of the
other structures and, accompanying them the two sides of
the heart are drawn backwards so as to lie side by side.
In the adult (fig. 54) the ventricles (ve. ) have fussd on
the midline, except at the posterior end, where the two

64

sides still project as somewhat hemispherical masses.
Hov/ever, internally the liimen remains divided (Tip;, 31)
through hall' oi' the extent of the ventricles. At the an-
terior end, th.e ventricle has the shape of an elongated
cone. The tv/o auricles accompany the ciUs in the poste-
rior development of the latter and come to lie side by
side like two large vessels, in the posterior half of the
pericardial cavity. Each projects into the ventricle on
its own side and valves separate the cavities of the au-
riclei^ from that of the ventricle (fig. 54).

The pericardial cavity of the "Ship-worm's "(figs.
10, 31, 32) lies on the apparent dorsal side of the vis-
ceral mass. It is very large, extending from the poste-
rior adductor to the visceral ganglion. In Xylotrya fim-
briata , it narrows in front to form a canal which projects
beyond the voider part to the posterior addii.ctor muscle.
About two- thirds of the distance from the visceral gan-
glion to the posterior adductor (fig. 10) the anterior end
of the ventricle dips down through the pericardium, into
the visceral mass. Th.is point is the end of the ventricle
and the beginning of the aortae , 'the end of the ventricle
being marked off by two semilunar valves which project

65

forwards on its dorsal and ventral sides (val. fif^.sc),
From the end of the ventricle two vessels are given off.
The larger (av.p. figs. 10,56) runs forwards (figs. 28-30)
in the visceral mass, and passes ventral to and in front
of the posterior adductor, to bond over tha latter and en-
ter the mantle as the large dorsal or posterior pallial
artery. Tiiis I'uns as a single vessel in Xylotrya at the
right side of the anal canal and epibranchial cavity (figs.
28-34, d.a.) to the posterior end of the body, v;here it
divides into the two paired arteries of the siphons. This
aortal have just described is the morphological posterior
aorta, though its course at first is anteriorly. The sec-
ond aorta' leaving the ventricle runs posteriorly in the
visceral mass and is the morphological anterior aorta.

The venous system consists of three important parts.
Blood from the viscera and anterior part of the body is
gathered into a system of afferent branchial veins con-
sisting anteriorly of large paired vessels (G.a. figs, 29
-31), which in the region of the visceral ganglion unite
to form the ver:/ large afferent branchial vein which mns
between the fused gills (figs, 10,32-34), Passing from
this vein through the gill lamellae, it enters tlie large

66

paired efferent branchial veins which enter the auricles.
Blood from the posterior part of the body is gathered into
an afferent renal vein (a.r.v, figs. 7)3,34) v/hich runs for-
ward and enters the pericardial spaces ,at the posterior
ends of the kidneys.

The description I have just given ajplios to X. fim-
briata and T, navalis. In T, norvegica, while the rela-
tions arc somewhat different, the homologies remain the
same. In this species, the principal part of the visceral
mass has remained more anteriorly and the posterior part
of the body is longer in proportion. In following the
gills, the heart has become much more elongated, and this
elongation has taken place in the aorta-like structure
which runs forv/ard from the more thickened portion of the
ventricle. In this species, the pericardial cavity ex-
tends much further forwards than in X. fimbriata, passing
under and anterior to tJie posterior adductor muscle as a
long canal, to end under the aesophagus. In it, the ven-
tricle runs to the anterior side of the posterior adduct-
or, to dip into the visceral mass. Valves mark the end of
the very long ventricle, from which tv/o vessels pass for-
wai'ds. The larger, after, giving off branches in its

G7

course, bends around the adauctor-, and divia^s into paired
pallial arteries which supj^ly the posterior part oi" the
body. This is the posterior aorta. TiiQ other, the ante-
rior aorta also runs forwards a short distance, but soon
breaks up in the viiiceral mass,

I have gone into details in describing the aortae ,
because the posterior aorta is described as fused with the
anterior in Teredo. This observation was first made by
Grobben (5) , v/ho described as aorta a part of the ventri-
cle which is distinctlj'- muscular and contractile. The
part that should have been described as aorta he has not
figured at all. Menegaux has also maintained that the t\'ro
aortae are fused (11). Unfortunately, neither of these
v/orkers names the species with which he v/orked, but their
descriptions of other parts are so faulty as to indicate
that there is little doubt that they have been in error in
this regard.

68

h. The Alimentary Canal.

In adaptation to their burrowing mode of life, the
alimentary canal of all the Pholadacea h.as liooonie nore
highly specialized, perhaps, than in any other type of
Lamellibranch. Th.is specialization is carried farthest
in the "Ship-worne".' .

I'lost of the parts of tl:e alimentary canal of the
adult are already present in the newly-attached larva,
though their relations to each other and their relative
development are very different. The general plan is shovm
in fig. 2, which represents a larva from the rirrht side
with the shell, mantle and gills removed. A long cil-
iated oesophagus (figs. 2,24, oe.) leads into a rather
small stomach, from which project on either side the two
large, simple liver lobules, composed of large^ coarsely
granular, pigmented, non-ciliated cells (figs. 2, 25). The
intestine leaves the right side of the stomach, (figs. 2,
26) and after forming a single loop passes over the poste-
rior adductor a3 the rectum. Just posterior to the intes-
tinal opening is a small hemispherical diverticulum of the
stomacli, the caecum (ce. figs. 2,25,26) composed of dense-
ly granular, non-ciliated cells. The posterior, ventral

G9

part of the stomach is occupied by the opening of a larfje ,
conical diverticulum which is median in position, the
sheath of the crystalline style (C.^j. j'igs. 2,24). Its
walls are composed of the larr;e, coarsely granular, dense-
ly ciliated cells characteristic of this structure, ex-
cept at the blind end, where the cells are smaller, more
finely granular and non-ciliated, (fig. 24).

The alimentary canal of the larva is interesting be-
cause of the advanced development of some parts and the
retarded development of otliers. The liver has advanced
but little in form beyond a stage reached two or three
days after hatching. On the other hand, the caecum of the
stomach, which is peculiar to the menbers of the Pholada-
rea, is already present as a rudiment, although it is not
to become ftmctional till after the adoption of the life
in the v/ood.

As the lai*va develops into the "Ship-worm" , the size
and relations of the parts of the alimentary canal change
greatly. The oesophagus becomes, in the adult, very short
in comparison with other parts (fig. 10). The stomach
elongates posteriorly more and more (figs. 4,7,:").) till
in the adult it projects far beyond the posterior adductor
and forms a long cylindrical tube (fig. 10). As is well

70

known, the wood -^rated away in boring, is invested and
stored in the caecum of the stomach. Even bel'oro the in-
gestion of t'no wood berins , the caeciim projects into the
foot as a large hollow vesicle, lined by clear, ciliated
cells. But, as soon as v;ood is ingested, it enlarges rap-
idly and soon forms the largest part of tlie alimentary
canal (figs. 4,7,10 Ce.). V/ith its increase in size, it
comes to leave the posterior end of the stomach, and
crowds the sheath of the crystalline stylo to the left
side (figs. 4,7,10). In young specimens, the caec^um occu-
pies almost the whole mass of the foot, and its blind end
points forwards (figs. 4,7). As the visceral mass elon-
gates, the caecum is gradually dravm backwards, till in
the adult, it forms a very long c^'lindrical tube, stretch-
ing to the posterior end of tlie visceral mass (fig, 10 (-e.)
In "nhip-worms" that are boring and grov/ing, the caecum is
always completely filled with ingested particles of v;ood.
The scarcity of diatoms and other food materials seems to
indicate that in the "Ship-v/orm" , boring and ingestion of
wood, and ingestion of food alternate , and that, when
feeding, tlie food is guided into the intestine; and when
boring, into the caecum. The caecum, then, is a long,

71

blind tubG, opening only at its anterior end into the
stoniacli. Internally it is lined by a ciliated nucus mem-
brane, v/hich is folded like a typhlosole (fifjs. 32,33),
but the fold seems of independent origin, and not at all
homolocous witli the fold in the intostine. The long re-
tention of woody particles in tlie caecum, along with the
greatly increased absorbent surface of the latter, indi-
cates tliat the wood is in part digested and serves as food-

In elongating posteriorly tlie caecum pushes the in-
testine ahead of it, so that the latter alvmys forms a
very long straight loop around the former. The intestine,
along v^ith the great development of the caecum, and the
greater development of the liver on the right side, in the
adult leaves the stomach slightly to the left of the mid-
line, near the posterior end (fig. 10). Bending forwards,
it foxTOS a single short loop and then passes backwards to
form theloop around the caeciim. Then passing dorsal to
the stomach it bends over the posterior adductor as the
rectum (r) wliich projects slightly into the anal canal.
Throughout its v/holo extent the intestine possesses a
typhlosole, but slightly developed, except in that part
next to the stomach. Here the typhlosole is so greatly

72

developed as to form several coils (rif;.29) which cause
the intestine in this region to be greatly enlarp;ed (fig.
10). The intestine of X.finbriata is very much shorter
than in other "Ship-worms". The shortening of the intes-
tine is doubtless connected with the greatly increased ab-
sorbent surface of the coiled typhlosole. In most "Ship-
worms " the intestine forms several coils before it passes
around the caeci:un and in such forms there is no ^reatly
coiled typhlosole.

In Teredo, as in Pholas , tr.ere is a second small,
quill-shaped caecum of the stomach on the dorsal side to
the left, under the posterior adductor (Ce. figs. V,10,
28). It is lined by columnar, ciliated cells and general-
ly contains particles of sand. It is small and seems de-
generate, but it may have some function at thepresent
time. Pelsenoer has observed an apparently homologous
structure in Ilucula, v/here it is said to secrete a small
style.

The sheath of the crystalline style, present on the
midline of the larva, comes to open from the left side of
the stomach near the anterior end of the latter (n.S, figs.
7,10), and hangs towards the right side. Its blind end

73

forms a vermiform tube, which is very dilTcrcr.t from the
rest of the slieath. The latter has its v/alls composed of
large coarsely granular, cells, v;hich bear very heavy,
dense cilia (fig. 57, A.). The tubular portion, on the
other hand, has its walls composed of elonr;ated, densely
granular and deeply staining, non-ciliated cells. In ad-
ults, the walls of the tube may become very thin (fig.
57 B. ) in jiarts. V/liat the f^inction of this tubular por-
tion is I aifl not able to state, though it is perhaps the
secrotion of ^ome constitLient of the style. Earrois (1)
has figured a pair of diverticula at the ends of the
sheath of Pholas dactylus , lined by cells similar to those
of the rest of the sheath. On examining sections of ap-
parently specimens of the same species, I find a tube, as
in Teredo , lined by cells of the same character as in the
latter, so that I am inclined to believe that Earrois' de-
scription and figures are faulty.

The liver, com.posed of a simple spherical lobule
on either side of the stomach in the larva, soon divides
into several lobules on eitlior side (1. figs. 4,7). As
groY/th takes place, the duct of the right half of the liv-
er divides (in specimens 4-5 rTi::. lomg) , and as the "Ship-

74

worm" elonf^ates, the posterior part of the ri^ht half of
the liver passes backwards, so tliat in ti t , its duct
opens into the posterior end of the stomach. The anterior
and posterior portions of the liver arn nornr;lotoly separa-
ted from each other, foiTninc separate liver masses (fig.
10). Tlie anterior remains in the foot, and sends its duct
to open into the external anterior portion of the stomach.
There seems little doubt that it xias this part which Frey
and Lenckart observed and described as the salivary r;lands
peculiar to Teredo. Tho posterior part of the liver is
the larger of the two, and opens by a very large duct into
the ventral part of the stomach. It is differentiated in-
to two portions, which in structure and apparently in
function, are quite distinct from each other, tliough they
open into the stomach by the same duct. The more elonga-
ted, slii^htly larger portion (fig. 30) lies on the right
side, and in structure is like the anterior liver mass of
Teredo and the whole liver in other forms of Lamellibranchs-
The second portion (fig. 30) lying more on the left side,
is different in appearance. Its lobules are larger, with

larger lumens and thinner walls, which are composed of
flattened less glandular cells. The presence of large

75

quantities of v/oody rarticioi: in these larr^er, uliin-walled
lobules su/^f^ests that this po^^tion oT the liver may be
speciuliiied for the dit^^estion oi' cellulose, and this view
is strengthened by the long retention of v/oody materials
in the caecuiii. This portion of the livor is adjacent to
the opening of the caecum, and it may be that it secretes
a ferment for cellulos digestion which is oontinuod in the
caecum. As has been pointed out already, the latter by
its structure seems adapted to absorption on a large
scale.

7G

i. The Nervous Syctem.

The nervous system oL' "Ship-worms" I have studied in
the larval and subsequent stages of Xylotry^i fimbriata,
and in the adult of T. naval is and T. norvegica. V/hile my
description ai plies especially to o: lirst oi i.-se, the
others are in such close agreement, that we seem justified
in believing that there is great uniformity in this regard
in all of the species of the Teredinidae , and that the de-
scriptions heretofore given have been erroneous.

The Nervous System of the Larva. - In the larva the prin-
cipal elenients of the adult are present. However, in
their relations to each other, their embryonic development
is not corqrlete; and in their relation to other structures
great changes take place along with the change in the gen-
ei*al organisation. The general plan i;^ r^hown in figs. 2
and 59, the latter representing a dorsal view of the ner-
vous system of a larva just attaclied. In front ^^ ...vi on
the sides of the mouth are the two cerebral ganglia, (c)
separated l" " •'■■••■ -hort co: ii lissure , and each sending a

77

connective to the pedal ganclion (r) ol' the same side. At
t'.ie side of tlie cerebral are the pleural ranprlia , distinct-
ly separated from them, and sending connectives posterior-
l3' to tlie visceral E^an^lia. I think thero in alno a pleu-
ro-pedal connective at this stage, out this I am not able
to state positively. The pedal ganglia at this stage are
as co^1l^letely fused as in the adult, o j just poste-
rior to the beginning of the oesophagus (fig. 24) . Lying
immediately in front of the j^osterior adductor muscle
(figs, 2,24, 26), the visceral ganglia form a long cylin-
der enlarged at both ends. The commissure here contains
ganglion cells, T'-^ ■^■o sides rapidly become more close-
ly ftised and in the early stage represented in fig. 4,
the concentration is almost as great as in the adult.
Each visceral ganglion of the larva gives off a respira-
tory nei've which bears a respiratory ganglion still far
apart from the visceral. TiVhile tlie visceral ganglia are
becoming more closely fused, the commissures between the
cerebral aad pleuial ganglia are becoming obliterated. These
ganglia persist as seperate masses in the young "Ship-
v.'orm" of three or four days (fig. 4), but soon afterwards
fuse completely, though sections of latter stages still

78

indicate by their structure the double origin of the so-
called cerebral ganglia.

V/liile these concentrations of the visceral ganglia
with each other and of the pleural with the cerebral have
been taking place, the cerebral commissure is constantly
elongating, along v;ith the grov/th of the oesophagus, so
that in t'ne adult, the cerebral ganglia are separated from
each ot;.;--' y a long commissure.

The Nervous System of the Adult. - Along with the great
change in the general relations of the various systems
that have taken place from the "Ship-worm" larva to the
adult, the nervous system has changed, principally in the
changed position of the visceral ganglia, which lose their
position in front of the posterior adductor, and come to
lie much posterior to it. However, the same three pairs
of ganglia are present in the "Ghip-worms" as in other
types of Lamellibranchs. The general arrangement is shown
in fig. 60. Lying almost at the sides of the mouth are
the two cerebral ganglia (c. figs. 10,60), well developed

79

and separated from each other by a lone conmiisnuro (c.c),
which is composed only of nerve fibres. From near the out-
er end of cither, a single large pallial nerve passes, to
be distributed to the anterior part of the mantle v;hich
underlies the shell, and forms the cephalic hood. From
near the inner ends of the ganglia large connectives pass
around the sides of the mouth to the pedal ganglia (p);
and, from the posterior outer ends, the cerebro-viscoral
connectives pass posteriorly to the visceral ganglia. The
pedal ganglia give off several pairs of large nerves which
innervate the foot.

The Visceral Ganglia. - The two visceral (v. fig. 10,60)
ganglia of the larva fuse into the single mass which lies
very far posteriorly in the adult (v. fig. 10). After leav-
ing the cerebro-pleural ganglia, their connectives with
the visceral pass along the sides of the "liead" under the
anterior gill filaments; but , posterior to the large adduc-
tor muscle, they take up a more median position, among the
tissues of tne liver and genital organs. In front of the
visceral ganglia they come to lie close together, internal

fiO

to the larce , duct-like portions of the genital organs.
But before entering the visceral ganglia, they pass dorsal
to a sraall "anterior ganglion" •./nich li t in front of
the latter. In passing it , they lose a Si . lount of
nerve fibres (fig. 63), v/hich are lost in it. Then the
connectives enter the visceral ganglia, but little dimin-
ished in size. This anterior ganglion '.vas first described
by Pelseneer (13) for the "Ship-worms" and seems peculiar
to them and their allies. It is a small ganglionic mass
lying distinctly in front of the visceral in well preserv-
ed specimens, and from the fibres crossing between the sids;
it seems composed of two halves, quite completely fused
together. As has been stated, the connectives in passing,
send fibres ventrally into it, to be completelj'' lost in
it. From this ganglion several pairs of nerves are given
off which innervate tho kidneys and other viscera, the gen-
ital papillae and the osphrodium, at least in part (fig.
60). From the anterior end, a pair passes forwards to sup-
ply the genital organs and perhaps other viscera. From
the middle of the ganglion a pair passes laterally to in-
nervate the genital papillae and the kidneys (fig. 63).
Leaving the posterior lateral angles of the ganglion, the

Rl

l&ngest pair of norves pass backwai-ds under t!ie visceral,
and divide each into two pai-ts. The one, somewhat larger
than the other, passes dorsally to enter, and be lost .in
the mass of the visceral £;;anglia. The other passes later-
ally to innervate the osphradium.

The visceral ganglia proper of the adult (figs. 10,
60), along with the greater development of the posterior
part of the body innervated by them, have attained greater
comparative size than the cerebral and pedal. They form
a somewhat three lobed mass, in which the larger, central,
part consists of the completely fused visceral ganglia of
the larva, v^hile the lobe on either side consists of the
respiratory ganglia v;hich have come to lie adjacent to the
visceral proper.

From the visceral ganglia several pairs of nerves
are given off, whose connection with the visceral is
through the lateral masses (fig. 60). Passing forwards on
either side are two small nerves (figs. 50,1,2) which ac-
company the kidneys and anal canal, which innervate the
posterior adductor and the anterior part of the mantle.
Given off slig^itly posterior to tl.em, a large nei've (3)
goes directly to the middle part of the mantle. Posterior-

';2

ly, a pair of lar^e pallial nerves (p.n. Vir,3, 33-. .5, GO)
passes backwards to innervate the posterior part of the
mantle, including the siphons and the muscles of the pal-
ettes. The branchial nerves (b.u.) pass laterally, close-
ly associated with the osphradiiom, and then innervate the
sills.

This description of tlie nervous system differs es-
sentially from that of Quatrefages (15) which has hereto-
fore been accepted. He thought the tvio cerebral ganglia
closely fused and the pedal rudimentary and separate. I
have no doubt that he mistook the pedal ganglia for the
cerebrals; his figures shov; this. But v/hat he observed
and figured as the two very small pedal ganglia I do not
know. It has been seen that while they are not so large
as in forms v/ith a large foot, they are not at all rudi-
mentary.

Otolith. - The larva leads an active locomotor life, and
some means for distinguishing the position of its posses-
ser is very essential. But the adult "Ship-worm" may as-
svime any position, and the otoliths become useless and de-
generate. After attachment, they soon cease to grow, -^-^^

in specimens two oi" threo nim. long, their function soGms
lost, though they persist as small masses of cells in the
adult.

Sense-Organ of the Genital Papilla. - Ono of the pairs
of nerves of the anterior ganglion has been described as
going to the kidneys and genital papillae. Situated just
at the junction of the ectodermal genital duct, with the
sexual organ there is an organ v/hich by its structure
seems to be for special sensation. The nerve to it (figs.
65,. 64) after a very short course is distributed to senso-
ry cells which lie adjacent to the epithelial lining of
the genital duct. The sensory cells are long spindle-
shaped, and send their peripheral ends to terminate among
the epithelial cells lining the genital duct. Their cen-
tral ends I have not traced into the nerve, but it seems
justifiable to suppose that this is their connection. What
the function of this organ is I cannot state. V-Tiile the
figures apparently show it somo distance from the exterioi;.
it should be remembered that in "Ship-worms" 30 cm. long,
the sexual duct is less than a half mm. long, and that the

R4

sense orcan is really verj' near to and for purposes of
sensation, practically at the surface.

The Osphradia. - These J,lolluscan orr;ans of special sense
fonn large masses of complex tissues at either side of the
visceral ganglion. (fig. 60) . Their general shape is ellip-
tical and they are in close association frith the branchial

nerves. Each organ (fig. 61) is composed of tvro parts.
At the ventral (outer) surface, there is a part of the
body epithelium, v/hich in this region is specially differ-
entiated from the surrounding cells. Y/hile the epitheliiim
of the epibranchial cavity is ciliated, the osphradial ep-
itheliiom is quite devoid of cilia. Besides, the cells
composing the osphradial epithelium seem to liave quite
lost their cell-walls, so that the spherical muclei lie in
a common mass of protoplasm. The outer surface of the
epithelial layer is covered by a very delicate membrane,
and at its internal surface there is a stouter basal mem-
brane. Underlying the surface epithelium is a mass of
nervous elements, composed of both cells and nerve fibres.

The cells, hov;ever, are sensory and stain somewhat dif-
ferently from the ordinary ganglion cells. These sensory

cells are of two kinds, both spindle-ijiiajjed ana scndinfj
their peripheral ends throuf^h the basement membrane of the
overlyinc epithelivun, to break up into brush-like termina-
tions just inside the delicate outer membrane of the epith-
elixim. These structures are shown in figs. 61 and 62,-
In fig. Gl, the two types of cells are shown, the larger
one to the left representing the type much less numerous
than the other, staining differently from them and pene-
ti'ating the osphradial mass to terminate centrally differ-
ently from the smaller, more numerous cells. The internal
or central connections I have not been able to determine,
but this much it seems justifiable to state. The osphra-
dial nerve from the anterior ganglion becomes so closely
associated with the respiratory nei^e, that it cannot be
stated that it alone supplies the osphadium. Also, the
large sensoiv cells penetrate through the osphradial mass,
and especially it cannot be stated that their connection
is v.'ith the osphadial nerve.

These structures I have described in detail for two
reasons. In the first place, the epithelium of the ospha-
dium is usually described as consisting of colvimnar cells,
v/hich form the sensory part of the structure. This I have

lb und to conaist oi' a layer iii vnuch ccii outimes are not
distinp:tiishable , and in which the spherical nuclei lie as
in sincytium. The real sensory cells are the spindle-
shaped cells lyinc in the deeper part of the osphradiiim.
In the second place, Pelseneer (10) has described
the osphradiiom in Teredo and Pholas as innervated by a
nerve from the anterior ganglion, and the latter as con-
nected with the cerebral ganglia tlirough the connectives.
From this he concludes that the osphradia, as v;-ell as the
other organs of special sense, are innervated from the
cerebral ganglia. The organization of the nervous system
in Teredo, it seems to me, lends no evidence whatever to,
this view. The nerve fibres received from the connectives
by the anterior ganglion are quite lost in the latter and
cannot be traced into any of the nerves v/hich leave it.
Moreover, the anterior ganglion may with much more reason
be said to be connected witli the visceral ganglion, for
the branch of the so-called osphradial norve from it to
the latter, is much larger than the nervous elements re-
ceived by it from the cerebro-viaccral coni^ectives. Pel-
seneer seems not to have seen the other nerves that leave
the anterior ganglion. V/ith as much reason it might be

87

said tliat the structures they suj^ply also are innervated
from t!ie cerebral ganrlia. . : ;'ibres, it !■!»: . ., pass
from those structures through the anterior ganglion to the
cerebral, but tliat the latter .i-- the only "■^"♦ves in
which reflexes may be established seems not in accordance
with the structure of the nervous system in Teredo. It
seems raore plausible to regard the anterior ganp;lion as a
part of the visceral v^liich has been separated from the lat-
ter. It receives a part of the cerebro-visceral connect-
ive, and gives off some of the nerves that formerly were
given off by the visceral.

From a theoretical standpoint, too, one would expect
elongated forms like Teredo and Pholas to have a more di-
rect connection. between the osphradia and the reflex cen-
tres. If the osphradia test the character of the water
flowing over the gills, then it is difficult to believe
that in a large "Ship-worm" the nerve impulse should
travel from them to the cerebral ganglion and back again
thi'ough the visceral ganglia to tliepallial nerves before
the siphons can be contracted and the inhalent current
stopped. This '.vould necessitate a course of almost two
metres in very large specimens. The more direct connec-

88

tion throu<3h the visceral gangii
reasonable to expect.

:e one it sooms

j . The Kidneys.

The kidneys (orj^ans of Bojanus, nephridia) of Teredo
were observed, apparently, by Deshayos , but mistaken for
veins. Quatrefages also observed them but gave no ade-
quate dosci'iption. Pelseneer (14) has noted the position
and relations of the openings of the tv/o ducts.

In the adult "Ship-worm" the paired kidneys lie on
the dorsal side of the large pericardial cavity and ven-
tral to the anal canal, extending the long distance be-
tween the posterior adductor muscle and the visceral gan-
glion. Each kidney consists of what may l^e termed the
body, which lies around the posterior face of the poste-
rior adductor mtiscle (k. , fig. 10); and two very long ducts,
one of v/^hich puts the body in communication with the peri-
cardial cavity, v/l.ile the otlier leads to the exterior, "i"^"^

89

body is a massive, much poiichod jtructure in v/liich tlie
lininf; secretory epithelium i'j vacuolated and in part cil-
iated. From the body the very long, narrov/, cylindrical
afferent duct passes posteriorly (ka. , figs. 29-31) near
the midline. Just in front of the viseral ganrlion it en-
larges, becomes convoluted internally, diverges from its
fellow of the opposite side (k.a fig. 66) and dips under
tlie end of the efferent duct (fig. 65) to open into the
posterior angles of the pericardial cavity (fig, 32) by a
large funnel-sliaped opening. The lining cells of the af-
ferent duct are not vacuolated and apparently not excreto-
ry; and, are not ciliated except in the enlarged, funnel-
shaped portion in which they bear strikingly long, dense
cilia (fig. 64) .

The efferent duct, loading from the body of the kid-
ney to tlie exterior, is also a cylindrical tiibo , of much
larger diameter than the efferent duct, It runs with tlie
latter near the mid-line (k.e., figs. 10,29-51) and in
front of the visceral ganglia , after diverging slightly
from its fellow of the opposite side (fig, 66) , it crosses
dorsal to the end of the afferent duct. Then it passes to
vcntrally and posterially (figs. 65,66) to open near the

90

midline into the epibranchial cavity, undGi* the vi::coral
Can^lion. The efferent duct is lined by coluximar, vacuo-
lated and apparently secretory cells, which are not cil-
iated except at the anterior end, and also neai* the exter-
nal opening.

Venous blood from the posterior end of the body re-
turns by an efferent renal vein (figs. 33,34, a.r.v.)which
runs in the mantle, and on a level v/ith the posterior ends
of the kidney duct, enters the peri-ronal blood spaces
(figs. 29-51). After bathing the kidneys, it enters the
general venous circulation.

Pelseneer, who, it seems, observed onlj'' the poste-
rior ends of the kidney ducts , described them as much pouch-
ed. In properly prepared specimens of X. fimbriata, I
find that, while the body of the kidney is much pouched,
the ducts form straight cylindrical tubes. Preserved
"Ship-worms" are almost always very greatly shrxxnken, and
I am inclined to believe that this fact accounts for Pelse-
neer's results. Also, contrary to the statements in text-
books (Lang) , I find that the two kidneys of X. fimbriata
do not communicate with eacli other, as they do in Pholas
and other foxras.

91

In the lai'va, the Kianeys lie antex'ior to the pos-
terior adductor muscle, and lateral to ti^o visceral gan-
glion (fifjs. ii,2G). As the viscoral []:an.'3lion passes under
and postei-ior to tlie muscle, the kidneys accompany it (fis;
7), In the early stages each kidney consists of a simple
loop (fic» 7) of vrhich the branch opening to the exterior
is the excretory. As the "Ship-v/orm" elongates, the chief
secretory portion of the kidney remains v/itli the muscle,
v/hile the two ducts become very long, and their openings
accompany the visceral ganglion.

k. The Reproductive Organs.

The first stage in which I have observed the repro-
ductive organs, is in specimens 2 mm. long, in which there
is a mass of germ cells under the visceral ganglion (g.o.
fig. 7). As growth takes place, processes grow oiit from
the original organ, till in the adult, the sexual organs
occupy a large part of the posterior part of the visceral
mass (figs. 10,31-33.). As the sexual rt'o^'-^cts develop,

they ai^G stored in the cavities or the organ and especial-
ly of that part first for-med {fif^s. G3,64, ov. ) wh.ich
serves as a duct for the rest of tho orf^an. The real
sexual d\act is remarkably short. It is formed as an ecto-
dermal invagination which is already present in specimens
2 mm. lonf^, but which does not break through till sexual
maturity.

In the adult Teredo, the sexes arc separate. How-
ever, young specimens (1-4 cm, long) of X. fimbriata are
very frequently hermaphrodite. As in all such cases the
sperms are developed first, it appears as if the species
-^ may be prolfiandrous . In the adults, I have observed no

external differences between tiie sexes. However, in the
male, there is a remarkable development of mucous gland
cells on the dorsal side of the epibranchial cavity; while
in the f eir.ale , they are not unusually developed in this
region.

1. Sximniary.

Tlie result of my viovk on Teredo may be siirimarized as
follows: T;ie larva of Toreclo is a typical f roo-s'iVinuninn
marine Lamellibranch larva. Tho vriiole veliun is suddenly
cast off and eaten, soon after the attachment of the larva.
After tlie loss of the velum the younc Teredo is a typical
small bivalve. The loss of the velum in Teredo and in Os-
trea (which I have also observed) , indicates that the for-
mation of the palps in Lamellibranchs has no connection
with the velum. A byssus apparatus is present in the new-
ly-attached larva. It is functional for but a few hours.
The position and relations of the sheath of the crystal-
line style in the larva indicate that this structure, in
the more highly specialized Lamellibranchs, is liomologous
with the posterior half of the stomach in forms like Yol-
dia and Ilucula. The pleural ganglion of the larva is sep-
arate from the cerebral.

The transformation of the Teredo larva into the
small "Ship-worm" is so rapid as to arioiint to a metamor-
phosis. Almost the whole organization is involved - sheH^
;..antle, foot, alimentary canal. The posterior adductor is
the effective agent iii I'orming the burrow, and tho shell

94

is the tool with which, it works.

In the "Ship-worms", i iio yo is a riarminx. gland in
the mantle of the posterior part of the body. A system of
hir;hly specialized muscles mar.ipulate che palettes and are
peculiar to Teredo. There is on either side but a half
ctenidium. The anterior ten filaments form small plica-
tions on the side of the "head", separated from the rest
of the gill by a long distance. In close association with
the gills is a prominent glandular structure of unknown
fi-inction. It consists of two typos of elements of remark-
able character.

Through the elongation of the visceral mass, the posi-
tions of the two aortae have been reversed; i.e., the ap-
parent posterior aorta is the real anterior, and the ap-
parent anterior the real posterior. The caecum of tlie
stomach is very large and apparently an important absorb-
ent organ. The blind end of the style sheath is tubular ■
and of very different character from the outer part. In
Xylotrya the typhlosole of the anterior part of the intos-
tine is remarkably developed.

The nervous system contains the ihi'ee pairs of gan-
glia, v/ell developed, as in typical Lamollibranchs. The

95

pedal f^an.f^lia are fused to^^ethor, the cerebral, separated
from eacli other by a lon/^ con-inissure. T:\n snwll "anterior
Canclion" innervates the kidneys, genital organs, and os-
ph.ralium in part. On the j^enital rlnct is an or^an of spe-
cial sense, oi' unknown function. The sensory colls of the
osphradiuni li^ >^eneath the surface ei^ithelium. Their
peripheral ends penetrate the epithelial layer, and break
up into brush-like toi'minat ions on its surface.

The kidneys lie dorsal to the pericardial cavity.
The main secretory ^■■.-.'t it: much pouched and lies on the
posterior adductor muscle. It is connected v/ith the pos-
terior ends of the pericardial cavity by a very long, nar-
roY/ duct, and with the exterior by a very long, larger
duct ' i ■:■! opjns under the visceral ganglion.

In the adult Teredo, the sexes are separate, iiow-
ever, young individuals (1-4 cm. long) of X. fimbriata aro
very frequently hennophrodite ; in all siacli cases the spenns
are always developed first, indicating that the species
may be protandrous. The sexual duct is very short and is
formed as an ectodennal invagination.

9G

Literature Specially used or ''•->• 1 t-, ^ -. the

Preparation of this Paper.

1. arrois, Th, Le Stylet Crystallin ;ics T,fimollii)ranches ,
Revue biol. du Nord de la France. vols. 1 and 2. 1889,90,

2. Deshayes , G.B. Kistoire Ilaturelle des Kollusques. (Ex-
ploration de I'Algerie) 1848,

3. E^ser, Ernst. .Touannetia cunningii, Sow. Eine rnorphol-
ogische Untersuchung, Arbeiten Zool. Institute Wurzburg.vol.
8, 1887.

4. Erlanger, R.von. Zur Entwickelung von Paludina vivipara.
Morph, Jahr, vol.17, 1391.

5. Grobben, Carl. Ueber die Pericardialdrtlse der Lamelli-
branchiaten. Ein Boitrag zur Kcntniss der Anatomie dieser
Molluskenklassen, Arb. Zool. Inst. Universit^t V/ein. v. 7,
1SS8.

G, Hatschek, B, Ueber Entv/ickelungsgeschichte von Teredo,
Arb, Zool. Inst. \Yein. v. 3, 1880.

7, ICorschelt ixnd Heider. Lehrbuch der vergleichenden Ent-
'.Yichelungsgeschichte der v/-irbellosen Thiere, Jena, 1890.

8, Lacaze-Duthiers , H. de. Morphologie des Acephales.
Anatomie de I'Arrosoir (Asporgillum dichotonrnvm. Arch. Zool.
Exper. , Ser. 2, vol. 1, l';o3.

9, Lane, Arnold. Lehrbuch der vergleichenden Anatomie.

07

English ti'anslation, 15596.

10. Lankestor, F.. Ray. Article Mollusca. l-incl. : rit.
9th. ed.

11. I.'.ener^aux , M .A. Sur Igs homolor;ios de different
organes du Taret. Comtes Rendu, vol. lOS.

12. Feck, R. Holman. The Structure of the Lamellibranchi-
ate Gill. Quar. Jour. L'licr. Soc. vol.17, 1^.77.

15. Pelseneer , • Paul. Report ol" the Ai^atomy of the Heep-sea
Mollusca. Challenger Reports, Part 74, ISSS.

14. - - Contribution a l' etude des Lanellibranches , Ar-
chives de Biol. vol. 11, 1391.

15. Quatrefages, A. de. Memoire sur le Genre Taret. Ann.
des Sciences Nat. Sor. 3, vol.11, 1849.

16. Rice, Edw. L. Die systematische verwerthbarkeit der
Kiemen bei den Lamellibranchiaten. Jen. Zeit. vol.31, 1S97.

17. Y^ilson, E.B. The Origin of the Mesoblast-Bands in
Annelids. Joiir. Morph. vol. 4.

18. Ziegler, H. E. Die Entv/ickelung von Cyclas cox'nea.
Lam . Zeit. f. ■Viss. Zool. vol.41, I'^-'.Rfj.

98

EXPLANATION OF FIGURES.
General Reference Letters

an. Anus.

a. a. Anterior adductor Muscle

a.c. Anal Canal.

a.g. Anterior Ganglion.

ao.a. Anterior Aorta.

ao.p. Posterior Aorta.

a. p. Posterior adductor Muscle.

a. pa. Adductor Muscle of Palette.

a.r.v. Afferent Renal Vein.

au. Auricle.

b.a. Afferent Branchial Vein.

b.e. Efferent " "

b.s. Blood Space of Gill Lamina.

by. Byssus.

b.g. Branchial Groove.

c. Cerebral Ganglion.

c.c. Cerebral Commissure.

c.s. Crystalline Style.

ce.. Caecum of Stomach.

ce. Secondary Caecum of Stomach.

99

c.h. Cephalic Hood of Mantle.

c.p. Coi-ebro-pedal Connective.

c.v. Cerebro-Visceral Connective,

d.D. Puct oi Liie iland ui' Deshayes.

d.a. Dorsal Ax-tery.

d.k. Dorsal pivatol Knot of the Shell.

ep.c. Epibranchial Cavity.

ep.ca. " Canal.

e.s. Exhalent or Anal Siphon.

f. Foot.

f.c. Frontal Cells of Gill.

g. Ctenidium or Gill.

g' . Anterior Gill Filainonts.

g.a. Ascending Limb of Gill . Filament .

g.d. Descending Limb of Gill Filament.

g.du. Genital Duct.

g.D. Gland of Deshayes.

gl.ep. Gland Cells of Epidermis.

g.o. Genital Organ.

i. Intestine.

i.f.j. Inter-f ilamentar Junction of Gill.

i.l.s. Inter-laminar Spaces of Gill.

i.s. Inhalent or Respiratory Siphon.

100

k. Kidney.

k.a. Afferent Tube of Kidney.

k.e. "rrr>rent Tubo of ICidney.

1. Liver. l.d. Liver Duct.

I.e. Lateral Colls of Gill.

If.c. Latero-frontal Cells of Gill.

lig. Shell Li,'3ament

m. r'antle.

m.c. '.' Cavity.

mu. Muscle Fibres.

o. I'.iouth.

oe. Oesophagus.

o.n. Osphradial Nerve,

OS. Osphradium.

ot. Otolithic Vesicle.

ov. Ovary.

p. Pedal Ganglion.

pa. Palotte.

p.c. Pericardial Cavity.

p.gl. Gland Cells of Foot.

pi. Pleural Ganglion.

p.n. ^ailial Nerve.

p.p. Protractor I'uscle of Palette.

101

r. Rectiun,

r.f. Retractor Muscle of Foot.

r.p. Retractor Muscle of Palette.

r.s. Reti'actor Muscle of Siphons.

s. Stomach.

s.r. Supporting Rod of Gill Filament.

s.s Sheath of Crystalline Sti/le.

V. Visceral Gan.'::lion.

vl. Valve of Anterior End. of Ventricle.

v.c. Velai" Cavity.

ve. Ventricle.

v.k. Ventral Pivotal Knob . of the Shell Valve,

v.m. Visceral Mass.

10 :i
Explanation of Figiirea.

Fis. 1, ^:ewly-at taclied . .i'v.. ,. . ... f imbriata. Sketclied
from life. The foot is shown fully extended. x220.

Fig. 2. Newly-attached larva, from the right side.- The
rir^ht shell, mantle and gills removed. The cells of the
disintegrating velum are not represented. The foot not fully
extended, x 320.

Fig. 3. Young "Ship-worm" of about three days attach-
ment, from the ventral side. The shell is reprosented as
transparent, to shov;- the underlying gills on the sides of the
visceral mass, x 250.

Fig. 4. Same stage as fig. 3, from the left side. The
left shell, mantle and gills represented as removed. The
double origin of the cerebral ganglion is still shown. The
visceral ganglion and kidney still lie in front of the pos-
terior adductor. The caecum fills the foot , and has crowded
the crystalline style and intestine to the loft side, x 250.

Fig. 5. Specimen of about one v/eek in the wood. The
worm-like form is becoming rapidly assumed, x 190.

.Fig, 6, Same stage as fig. 5, ventral vicvr. To show the
arrangement of the gills and the extent of t--'^ visceral mass.
X 190.

Fig. 7. Same as fig. 5, the left sliell, mantle and gills

lo:

removed. The pericardial space witli the included parts, has
taken up a position postcriu.- .^ thn ^.'i.ii.^i ,, • :.,3cle. The
secondary caecim of the stomach has been fonned. The ciUs
project beyond the visceral mass, x 190,

Fig. 8, Adiilt , from left side. Tho two extensions of
the mantle over the shell shown on thn dorsal side of the
latter. The mantle also extends over the posterior margin of
the shell for a short distance. The siphons ai"e represented
as fully extended, but the palettes not quite fully retract-
ed. The mantle extends over the bases of the palettes as a
collar . The attachjiients of the muscles of the palettes and
siphons are shovm. The drawing v^as made from a slirtitly con-
tracted specimen 10 cm. long.

Fig. 9. Same as S, the mantle removed to its line of at-
tachjtient dorsally, at tlio two ends, to the midline.

Fig, 10. Adult, anterior half of the body, with the left
shell valve, mantle and gill removed, and the pericardial
cavity laid open. }Ialf of the posterior adductor removed.

Fig, 11, Ri^ht^ and fig, 1?., left shell valves of newly-
attached larva, internal vicv/. Tlie rudimentary apophyses are
shown below the teeth, x 220,

Fig. 13, Shell of newly-attached larva, end view, x 220-

.Fig, 14. Shell of "Sh.ip-worm" that has been in the wood

104

about one day, front view. The first row oi' teeth, apophyses
and pivotal '-.'.lobs have been fori'ied. '!" ^-i ..i i ,^,^3 at both
ends. X 220,

.Fie. 15. Left shell valve of specimen about 1 mm, lon,^.
Oblique view. Tlie larval shell still shown, x 220,

Fig, 10. Left shell-valve of specimen 5 nim. lon^. x 45.

Fig, 17. Left shell-valve of adult, x 15.

Fig, IS. Front view of shell of adult. x 15.

Fig. 19. Internal view of i-ight valve, x 15.

Fig, 20, Left palette of specimen 5 mm, long, x 140.

Figs. 21 and 22, Diagrams of the posterior end of body
of adult, left side, to shovr the arrangement of the siphons
and palettes^ and their muscles. In fig. 21 the siphons are
represented as extended, the palettes as retracted; in fig,
22, the siphons are represented as contracted, the palettes
as protracted.

Fig, 23. Dorsal gland of the posterior part of the man-
tle. Section of whole gland of specimen 5 mm. long. The
letters are j laced in the epibranchial cavity. x 850.

Fig. 24, Sagittal section of a newly-attached larva.
The very large glands of the foot occupy a large part of the
mass of the latter. A large quantity of material derived
from these glands lies adjacent to tlie byssus gland. The

105

disintegrating cells ol" voluin, some ol' which have been eaten,
are not represented, x u60.

Fig. 25. Transverse section of larva. From a specimen
in which the luoi was i:ioru iru L rac tod tii-a:; in iij. 24, The
ventral r.iantle edre is filled with cells gorged with materi-
al, evidently for the I'apid growth or the shell -^ -^ its
transformation, x JGO.

Fig. 26. Horizontal section of specimen in which the
cavity of the velvim was partially obliterated. On the left
side the contents of the gland of Deshayes are sliown; on the
right side, the duct, x 660.

Fig. 27, Transverse section of a specimen 1 mm, long, to
show especially the extent and relations of the gland of De-
sliayes. x 250,

Figs, 28-35. A series of transverse sections of a spe-
cimen 10 cm. long, along the lines indicated in fig, 9. The
drawings were made with the aid of a camera and afterwards
touched up, though not essentially changed. The details of
structure are semi-diagrammatic. The rir;ht side in the sec-
tions is on the left side of the observer. All x 30,

Fig, 28. Section through the posterior -" --tor muscle
and cephalic hood. Tubular part of style sheath to the right
side. Posterior aorta asyinmetrical , on the right side.

lUi>

Fig, 29. Section through tlie round typhlosole, canal-
like anterior end of pericardial cavity and posterior end oV
the body oi' the kidney.

Fig. 30. Section tla rough the large, posteiloi* liver
mass. Shows the distribution and character ol" the two dif-
ferent parts.

Fig. 31. Section through tlie large ventricle and the
ovai-y*

Fig. 32. Section through the opening of the kidney into
the pericardial cavity, the anterior ganglion and ends of tho
auricles. The two arrows from the right indicate the course
of the v/ater currents between the gill laminae; the one
pointed dorsally, that of blood through the gill lamina. The
number and distribution of the inter-laminar connections in-
dicated by dots.

Fig. 33. Section near the posterior end of the visceral
mass.

Fig. 34. Section to illustrate the structui'C in the long
region botv/een the visceral mass and muscular collar.

Fig. 35. Section thi-ough the "collar", palette handles
and base of the siphons.

Fig. 3G, Section of a palette handle and its sheath. Tho
attachment of tlie ventral retractor muscle is shown, x b44.

107

Fig. 37. Lamina of (^ill oi" T. navalis, to show especial-
ly the distribution or tb.e glands of Doshayos , in which the
elements are represented semi-diap;rami!iatically. The arrows
indicate the course of the water anrl lilood ciirronts over the
lamina. The epibranchial cavity and the blood vessels are
indicated by the letters v/hich are jilaced in tJiese spaces.
X 312.

Fig. 38. Transverse section of three laminae almost in
the line of the louver arrow in fig. 32. Tvra interlaminar
junctions are shown. The two elements of the gland of De-
shayes arc shown, both as to character and distribution.
X 312.

Fig. 39. Tangential section of a gill to sh.ov/ the dis-
tribution of the inter-laminar junctions, x 312.

Fig. 40. Transverse section of three gill laminae, along
the line shov/n in fig. 37, near the tip of the lamina, so as
to sho\r the interlaminar junctions on one side, x GGO.

Fig. 41. Section of the three most anterior gill fila-
ments at the side of the "hood". The one to the left is only
a half filament. The letters are placed in the epibranchial
canal, x 860.

Fig. ; • . Group of cells from, the branchial groove at the
edge of t?ie gill, showing the character of the ciliated r-nlls

lOS

and the mucus colls among them, x 1900,

Fig. 43. Section of the branchial r;roove Y/hich connects
tiie two parts of the gill, x 860.

Fig. 45. Section of tlie duct of the gland of Deshayes
between the two parts of the gill. The epibranchial canal is
shown to the left and the afferent branchial vein to the
right. The groat variety in the cells in the duct, is ropro-
sented. x 1390.

Fig. 4G. Secition of two tubes of the gland of Deshayes,
from a gill la:;;ina. In t?iG walls of the gill lai;iina are
shovm sections of the dendritic processes which penetrate
among all portions of the glandular structures, x 1390.

Fig. 47. Coarser and fig. 4S , finer portions of the den-
dritic ]■ recesses from the gill lamina of T. navalis represen-
ted in fig. 37. The distribution and contents of these
structui'es ar'e represented in detail, x 1900.

Figs. 49-52. Four stages in the development of the struc-
tures of the second factor of the gland of Deshayes. x 1900.

Fig. 53. Ileax't of specimen 2 mm. long, dorsal view.
Openings from auricle show througli the walls of the ventri-
cle, X 360.

Fig. 54. Heart of young adult. The antei-ior aorta is
represented as turned to one side, and the auriculo-ventric-

109

ular valvos as showing thx*ouf;h the vessels of the ventricle,
X about 20.

Fig. 55. Longitudinal section of the ventricle and ves-
sels oi" a specimen 4 inin. long. Tlio a t-rows indicate the
course or the blood. The posterior adductor ntuscle, and the
wall oi" the stomach represented in part, x :"44.

Fig. 56. Longitudinal section of the anterior part of
the ventricle and vessels of a specimen 10 cm. long, x 544.

Fig. 57 A, group Oi' cells from the main portion of the
style slieath, and 57 E, from the tubiilar portion, x 1150.

Fig. 58 A, group of cells from the liver which show the
usual liver structure, and 58 B, from its modified portion.
X 1150.

Fig. 59. Nervous system of nev/ly-attached larva, showing
the pleural ganglion still separate from the cerebral, and
the visceral ganglia still wide apart, x P>60 ,

Fig. (50. Nervous system of adult, dorsal view, except
that the pedal ganglia are shown more from behind.

Fig. Gl. Section of the osphradium, vertical to the sur-
face, to show the structure of the osphradium and the two
types of sensory cells, witli their brush-like tenninations.
X 2420.

Fig. 62. Tangential section o^ ^hr> osvihradium, to s'r.ow

110

tlie distribution of the processes ol" tlie sensory cells among
the nuclei of the epithelial layor. x 1900.

Fig. 63. Transvei'se section oi' the anterior r^anr;lion. and
genital duct, to sliow t'-'.e connection bctv/eon t!ie corebro-
visceral connective and anterior ganglion; and the origin of
the sensory nerve and its distribution to the genital duct.
Only a part of the sense organ was included in the section,
v/hich is from T. navalis , though it miglit represent X. fim-
briata equally v^ell. x 544.

Fig. G4. Longitudinal Section of the genital duct, to
show its extent and character, and the sense organ of the
genital duct. The end of the ovary is shown, as also the
folded kidney near its pericardial opening. X 544.

Figs. G5 and G6. Diagrams to show the relations of the
ends ol" the kidneys, genital duct, pericardial cavity and
visceral ganglion. Fig. G5 lateral, and fig. o6 dorsal view.

VITA.

Charles Peter Sigerf oos , son of Geo. \'l. and Nancy
Sicerfoos, was born the 4th. of May, 1855, near Arcanum,
Ohio, where he lived and attended the public schools from
1S72 to 1882. The fall of 18S8 he entered the Ohio State
University, where he spent two years in preparation, and
four years in college, graduating in 1889 as S.B. Since
graduating he has been occupied as follows: During the
college years 1889-91, he was Assistant in Zoology and
Comparative Anatomy in the Ohio State University; 1891-2,
Instructor in Biology in the University of Virginia; 1892-
5, a graduate student, and 1S95-7, Assistant in Zoology
and Embryology, in the Johns Hopkins University. During
the summer of 1S93, ho v;as v/ith the Johns Plopkins Marine
Laboratory in Jamaica; and during the summers of 1894-5-6,
at Beaufort, llorth Carolina. Ilis ciiiof subject has been
Zoology, and his subordinate subjects Animal Physiology
and Animal Pathology.

Johns Hopkins University,
Baltimore , Md.

^^^It

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