NATURAL HISTORY OF THE SHIP-WORMS. 219 
liver passes backward, so that in the adult its duet opens into the posterior end 
of the stomach. These anterior and posterior portions of the liver are completely 
separated from each other, forming separate liver masses (fig. 10). The anterior 
remains in the foot and sends its duct to open into the lateral anterior portion of 
the stomach. There seems little doubt that it was this part which Frey and 
Leuckart observed and described as the salivary glands peculiar to ship-worms. The 
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 into two portions, which 
in structure and apparently in function are quite distinct from each other, though 
they open into the stomach by the same duct. The more elongated, slightly larger 
portion (fig. 28) lies on the right side, and in structure is like the anterior liver mass 
of ship-worms and the whole liver in other forms of lamellibranchs. The second 
portion (fig. 28), 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 
cells glandular in appearance. The presence of large quantities of woody materials 
in these larger, thin-walled lobules suggests that this portion of the liver may be 
specialized for the digestion of cellulose, and this view is strengthened by the long 
retention of woody materials in the cecum. ‘This portion of the liver is adjacent 
to the opening of the cecum, and it may be that it secretes a ferment for cellulose 
digestion which is continued in the cecum. As has been pointed out already, the 
latter by its structure seems adapted to absorption on a large scale. 
NERVOUS SYSTEM. 
The nervous system of ship-worms I have studied in the larval and subsequent 
stages to the adult of Xylotrya gouldi, and in the adult of T. navalis and T. dila- 
tata. While my description applies especially to the first of these, the others are 
in such close agreement that we seem justified in believing that there is great uni- 
formity in this regard in all of the species of the Teredinide, and that the descrip- 
tions heretofore given have been somewhat erroneous. 
Nervous system of the larva.—In the newly attached larva the principal ele- 
ments of the adult nervous system are present. In their relations to each other, 
however, the embryonic development of these is not complete; and in their relation 
to other structures great changes take place along with the change in the general 
organization. The general plan is shown in figures 7 and 59, the latter representing 
a dorsal view of the nervous system of a larva just attached. In front of and on 
the sides of the mouth are the two cerebral ganglia (c), separated from each other 
by a very short commissure, and each sending a connective to the pedal ganglion 
(p) of the same side. Lateral to the cerebral ganglion of each side is the pleural 
ganglion, still distinctly separate from it and sending a connective posteriorly to the 
visceral ganglion. I think there is also a pleuro-pedal connective at this stage, but 
this I am not able to state positively. The two pedal ganglia are as completely 
fused together as in the adult, and lie just posterior to the beginning of the csopha- 
gus (fig. 22). Lying immediately in front of the posterior adductor muscle (fig. 7, 
22, 24), the two visceral ganglia together form a long cylinder enlarged at both 
ends. The commissure connecting the two ganglia contains ganglion cells. The 
two sides rapidly become more closely fused and, in the early stage represented 
B. B. F. 1907—15 
