218 BULLETIN OF THE BUREAU OF FISHERIES. 
seems of independent origin, and not at all homologous with the fold in the 
intestine. The long retention of woody particles in the cxcum, along with the 
greatly increased absorbent surface of the latter, indicates that the wood is at 
least in part digested and serves as food. 
In elongating posteriorly, the caecum pushes the intestine ahead of it, so that 
the latter always forms a very long loop around the posterior end of it. In the 
adult the intestine, because of the great development of the cxcum and the 
greater development of the liver on the right side, leaves the stomach slightly to 
the left of the midline, near the posterior end (fig. 10). Bending forward it forms 
a single short loop and then passes backward to form the loop around the cecum. 
Then passing forward dorsal to the stomach it bends over the posterior adductor 
as the rectum (r), which projects slightly into the anal canal. Throughout its 
whole extent the intestine possesses a typhlosole, but slightly developed except 
in that part next to the stomach. Here it is so greatly developed as to form sey- 
eral coils (fig. 27), which are analogous to the spiral valve of the intestine of elas- 
mobranchs. Because of this the diameter of the intestine in this region is greatly 
enlarged (fig. 10). The intestine of Y. gould: is very much shorter than in other 
shipworms. This shortening is doubtless connected with the greatly increased 
absorbent surface because of the coiled typhlosole. In most shipworms the intes- 
tine forms several coils before it passes around the cxecum, and in such forms there 
is no greatly developed typhlosole. 
In ship-worms, as in Pholas, there is a second small, quill-shaped cecum of the 
stomach on the dorsal side to the left, under the posterior adductor muscle (ce’, 
fig. 9, 10, 26). It is lined by columnar, ciliated cells and generally contains par- 
ticles of sand. It is small and seems rudimentary, but it may have some function 
unknown at the present time. Pelseneer has observed an apparently homologous 
structure in Nucula, where it is said to secrete a small style. 
The sheath of the crystalline style, present on the midline of the larva, comes 
to arise from the left side of the stomach near the anterior end of the latter (ss, 
fig. 9, 10), and hangs toward the right side. Its blind end forms a vermiform 
tube, which is very different from the rest of the sheath. The latter has its walls 
composed of large, coarsely granular cells, which bear long, very heavy, dense 
cilia (fig. 56). The tubular portion, on the other hand, has its walls composed 
of elongated, densely granular and deeply staining, nonciliated cells. In adults 
the walls of the tube may become very thin (fig. 57), in parts. What the func- 
tion of this tubular portion is I am not able to state, though it is perhaps the secre- 
tion of some constituent of the style. Barrois (1889) 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 specimens of Pholas of apparently 
the same species as those studied by Barrois I find a single tube, as in ship-worms, 
lined by cells of the same character as in the latter. I am inclined to believe that 
Barrois’s description and figures are faulty. 
The liver, composed of a single spherical lobule on either side of the stomach 
in the larva, soon divides into several lobules on either side (J, fig. 8, 9). As growth 
takes place, the duct of the right half of the liver divides (in specimens 4—5 mm. 
long) and as the shipworm elongates, the posterior part of the right half of the 
