62 CALIFORNIA ACADEMY OF SCIENCES. 



line, but is thrown off considerably to the right. (The 

 figure represents the parts as seen from within the branch- 

 ial basket.) It appears from Garstang's figure that there 

 may be a tendency of this kind in P. Listeri, but he says 

 nothing about it in his description, and certainly if it were 

 so strikingly true as is the case in this species, he would 

 not have failed to mention it. 



There is a distinct thickening of the lip of the peri- 

 pharyngeal groove in the vicinity of the opening of the 

 duct, and at a high focus, when the structure is seen from 

 the inside, it is found that the wall of the duct becomes 

 continuous with this lip of the groove (figs. 15 and 21, 

 pi. ii, d. t. and ^. h. g.) By the same figures it is seen 

 that this thickened lip of the groove makes a U-shaped 

 bend at this point, in the median line, the convexity of 

 the U being directed posteriorly, or toward the ganglion. 

 The mouth of the duct is always, so far as I have ob- 

 served, at the right of the U. The " raised triangular 

 area whose apex is posterior," mentioned by Garstang, 

 is probably represented in my fig. 21 by the thickened 

 posteriorly curved band behind the U. Although at a 

 high focus the lip of the peripharyngeal groove is con- 

 tinuous with the walls of the duct (fig. 15), at a deeper 

 focus this continuity is lost, while the outlines of the 

 mouth of the duct are still distinct, thus indicating that 

 most of the orifice of the duct is dorsal to the lip. 



4. DIGESTIVE TRACT. 



Concerning the position and relations of the digestive 

 tract as a whole, I have nothing to add to what is well 

 known as "pertaining to the other species of the genus. 

 In several details of structure, however, there are addi- 

 tional facts that deserve to be dwelt upon somewhat. I 

 have been surprised that all the published figures of this 



