HETEROPLEURON HECTOEI, NEW ZRALAND LANCELET. 277 



chambers contain '' paired fin rays." In specimens collected 

 in Port Phillip, and presented to me by Prof. Dendy, I find, 

 on the contrary, most definitely only a single series of 

 fin rays in the ventral fin in this species. 



This continuity of the fin rays post-anally seems to show the 

 probability that the "ventral fin" is a part of the "median 

 fin/' as is suggested by Lankester and Wille}^ (p. 456), in 

 opposition to the earlier view by the former author that the 

 venti-al fin is the result of fusion of a paired structure 

 (3, p. o73). It becomes more evident that the double fin rays 

 of A. lanceolatns are secondar}^, arising perhaps as a result 

 of splitting of single rays. 



The pre-oral hood is much deeper on the right than on tlie 

 left side, so that when viewed from the latter aspect both 

 margins and their cirri are visible (fig. 2), and the vestibule 

 opens distinctly on the left side of the animal. This is even 

 better seen in a ventral view (fig. 4), where the right hood is 

 seen passing obliquely forwards to be continued into the 

 ventral fin, while the left margin disappears from view as it 

 curves dorsally upwards. 



In the drawings of Heteropleuron and Asymmetron given 

 by Kirkaldy and AndrcAvs ^ the vestibule and its opening are 

 represented as being quite symmetrical. It is ol' interest 

 that in this new species a condition is retained which is a 

 distinct reminiscence of the larval state of affairs. Further, 

 the cirri on the right side are somewhat shorter than those 

 on the left. These cirri number nineteen on each side, with 

 one median ventral, which is shorter than the lowest of the 

 lateral series ; these commence as long filiform structures, 

 and gradually diminish in length as the series approaches 

 the dorsal termination. 



The gonads, present only on the right side, appear to be 

 about eighteen in number, but as they dropped away from 

 the body-wall as it was turned aside there may have been a 

 few more. 



1 "All Uiidescril)e(i Acraiiiate — Assymnietron lueayauum," 'Stud. 

 Biol. Lab., J. H. Univ.,' v. 



