T E R 



22-2 



T E R 



On the opposite ride of the head the shell* were united 

 by a ligament from which they were readily separated ; at 

 this part were two small tooth-like processes, om- 

 the narrow edge of each shell, where the) were joined 

 together. 



From the middle of the exposed part of the head pro- 

 1 a land of proboscis; which in the living animal nad 

 a vermicular motion: its extremity was covered by R 

 cuticle not unlike Ihe cornea of the c\e. On removing 

 this, the cavity immediately beneath it wax found to cou- 

 tain a hard brown-coloured gelatinous substance, like n 

 Florence flask, with the lame end uppermost in form. Sir 

 Everard remarks that as this proboscis has no orifice, there 

 is reason to believe that it adheres to the wood, acting as a 

 centre-bit, while the animal is at work with the shell, and 

 thus the canal in the wood is perfectly eylindrieal. The 

 month was nearly concealed by the projection of tl: 



Is, but, when exposed, presented a very distinct round 

 orific. i the proboscis and the large digastric 



muscle. 



' The body of the worm,' proceeds Sir Everard, ' is in- 

 closed in one general covering, extending from the base 

 of the boring shell, with which it is firmly connected to 

 the root of the two small tubes, which appear out of the 

 wood. It terminates in a small double fold forming a cup, 

 o;i the inside of which are fixed the long small stems of 

 two opercula, which become broad and flat towards their 

 other extremity. These, when brought together, shut up 

 'sell, and inclose the two contracted tubes within it : 

 not one opcrculum corresponding to each tube, but in a 

 transverse direction. In the Teredo gigantea, the oper- 

 cula are similarly situated, each shutting up one-half of 

 the bifurcation. At the base of this cup the general cover- 

 - thick and ligamentous, for about one-fourth of an 

 inch in length, where the stems of the opercula are con- 

 '1 with it ; and at one spot of this thickened part 

 there is an adhesion to the cylindrical shell, which is the 

 only part of the animal connected with it. There is a 

 depression in the shell pointing out this spot. The double 

 fold of the outer covering, that forms the cup, contains the 

 sphincter muscle, which closes the orifice by bringing the 

 opercula together. The general covering is compi 

 two membranes, the outer the strongest, .and made up of 

 circular fibres, the inner much finer, having no fibrous 

 structure. On the back of the animal, this covering is 

 firmly connected to the parts underneath, and is there 

 strongest. On the belly it forms a cavity, and is thinner. 

 It i- everywhere sufficiently transparent to show the differ- 

 ent viscera through it.' 



Sir Everard Home began his dissection by dividing this 

 covering and exposing its cavity, into which there are two 

 natural opening*: one, that of the largest of the above- 

 described tubes, by which it receives the water from the 

 sea ; the other, a transverse slit under the union of the 

 boring shells, one-quarter of an inch long, opening into the 

 space before the mouth. The author states t hat the smaller 

 tube has no communication with this cavity, and that there 

 is none between this cavity and that of the belly, the vis- 

 cera having a proper covering of their own : the breathing 

 organs however, which are attached on the posteri< 

 face of this cavity, are described as having their ) 

 edge loose and exposed to the influence of the salt 

 so that the larger tube is constantly applying salt water to 

 them, and conveying it to the animal's month through the 

 aperture for that purpose. 



Digestive tiyitem. The head and abdominal viscera 

 were found to occupy about one-third of the animal's 

 length, the breathing organs another (bird, and the 

 between their termination and the ends of the small tubes 

 the remaining third. The oesophagus was very short, 

 lying on the left side of the neck. On the right w, 

 large approximated eland- connected with its coat. The 

 n-sophagus gradually swelling out became stomach, which 

 externally appeared as a large hair, extending the whole 

 length of the abdomen; the intestine commenced ch.se to 

 the termination of the oesophagus; but when (lie stomach 

 was laid open, a septum appeared dividing it into t\vo dis- 

 tinct bags, except at the lower end, where they communi- 

 cate. It may therefore be said, observes Sir Everard. to 

 be doubled on itself. In those worms which w era exa- 

 mined alive, the stomachs were quite empty : but in 

 preserved specimens the content* were a yellow-coloured 

 pulp, of which we shall have to say more presently : the 



quantity in a specimen from the British Museum was about 



intestine was very small, and became dilated into a 

 containing a hard, white, globular body, oft!" 

 of a large pin's h. -ad, and then made a turn upon itself. 

 Here the liver is attached ' ach, to which it firmly 



adheres. The gut passed forwaids till it reached tin 

 tral line of the stomach, opposite tb. 

 lined its course along that viscus, passing roum 

 end and np again on the opposite si. 

 tinned on one side of the oesophagus near!;, 

 mouth, where it was reflected o\er the middle ten*: 

 the digastric muscle of the boring shells, and ran along 

 the back of the animal, till it terminated in the small 

 through which its contents arc emptied. 



N//>/W. The heart was 



found in the middle between the mouthand the lower end 

 Of the stomach, and was situated on the back of the ani- 

 mal. There were two auricles, composed of a thin dark- 

 coloured membrane, which opened by contracted valvular 

 orifices into two white strong tubes, which united to form 

 the ventricle. This ventricle, Sir Everard observes, may 

 be -aid to be continued into an artery, which supplies the 

 viscera, and ascends to the muscles of the two boring 

 shells. The heart was very loosely connected to th< 

 rounding parts: its action was distinctly m i the 



external covering, and was observed, in some 

 after it had been laid bare. The first contraction was in the 

 two auricles, which shortened themselves in that action. A 

 swelling of the ventricle, followed by a com 

 thus produced. Sir Kverard found that ' from 



the ventricle could be traced up to the head, and the 

 vessels from the auricles were seen very distinctly as far as 

 the breathing organ-. The auricles were lined with a 

 black pigment, so that their contents could not be 

 through them ; and the coats of the ventricle were too 

 thick for transparency: but the muscle of the bonne- 

 shells was of a red colour, as well as the liver, and most 

 of the surrounding parts between the heart and the head. 



Sir Everard observes, that this structure of the Irpart ad- 

 mit-, only of a single circulation, as in other animals which 

 breathe through the medium of water, but that the mode 

 of its being performed is different from that in fishes: in 

 the Ti'riiliin^. lie remarks, the blood passes directly from 

 the heart to the different parts of the body, and returns 

 through the vessels of the breathing organs to the heart, 

 while in fishes it goes first to the breathing organs, and 

 then to the different parts of the body. This peculiar cir- 

 cnlntion, he adds, becomes a link in the gradation of the 

 modes of exposing the blood to the air in different ani- 

 mals : it appears to be less perfect than in fishes, since 

 the exposure to the air is carried on more slowly, but is 

 more perfect than in caterpillars. 



Brain andNn ' m. Sir Everard doubts not the 



existence of the brain and nerves in animals so perfect in 

 their organs as the Teredines, but he failed to detect them 

 during bis inv estimation. 



(li'niTiitirr Si/\trm. Sir Kverard Home describes the 

 testicles as two Ions glandular sub-' on each 



side of the stomach, of a whitish colour and granulated 

 structure. From each of them a duct passed to the ovaria, 

 which lay between the two breathing organs. The ducts 

 ran upon their outer edge, and terminated near the base 

 of the small tube. In this way, he remarks, t! 

 impregnated before they pass out at that orifice. In the. 

 worms from Shcerncsa, examined in February, tin 

 tides were small, and no appearance of a M be 



. but in specimens from the Hnnterian .Museum the 

 testicles were much fuller, and the o. 

 tiin-t longitudinal ridges: these, \\lien examined under 

 the microscope. ' in innumerable small 



When the ovaria are empty. Sir Ev . - that 



there is nothing to be found between tb- -ihing 



organ* but the small seminal vessels. He then adverts to 

 the statement of Scllius. who says that the nilix 



ria full of eggs in the spring and summer; that 

 cuiet with as late rs December ; but that those 

 individuals which he examined in February had their 

 ovaria flaccid and empty. 



With regard to T- < the same author ob- 



serves that, when arrived at ii- full growth, it clos, 

 tin- end ol md so <!u, SttB/M. Sellius 



believed that the animal by this act formed its own tomb, 



