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- 



