144 



BIOLOGICAL LECTURES. 



XT f 

 ' f 



10 



Predomi- From this table we learn that more than 



Dental nant Num- 



seven-tenths of the entire number of indi- 

 viduals belong to three groups, and over 

 half of these belong to the group in which 

 10 teeth occur in both rows oftener than 

 any other number. We have to do with a 

 reduction in the primitive number of teeth. 

 So much for the California specimens. 



The Chilian specimens seem to average a 

 larger number of teeth, for Girard counted in 

 his type specimen of 14 gills yf |yj, while 

 Putnam found H|j| or if if in the ma- 

 terial he studied from Talcahuano Bay, 

 brought to this country by the Hassler expe- 

 dition, which is reported as having 10 gills. 

 Lockington gives the formula as ^ I L, 

 which harmonizes with what I find to be the 

 most abundant formula. Lacepede's example 

 from Chili had a dental formula of Jy 1 - 1 y , 

 which is quite unusual, and indicates what 

 we may expect from a careful study of a 

 large series from the South American coast. 

 I fear that the dental formulae published in 

 the systematic accounts of Bdellostoma are 

 based for the most part on counts of the 

 teeth of one side of tlie tongue only, and in 

 this way only can I account for the bilateral 

 symmetry which characterizes them. 

 The reproductive organs of Bdellostoma are extremely simple 

 in their structure, and are composed in both male and female 

 of a simple, double-layered plate of the peritoneum which 

 hangs down as a fold from the dorsal wall of the body cavity 

 on the right side of the median line (Fig. 12). The ovary 

 occupies nearly the whole extent of the body cavity in the 

 female. The testis occupies only the posterior part of this 

 long fold, and in the female no eggs are developed in this 

 region. In hermaphrodites the two divisions of this organ are 



11111 



TO I TO" 



H1HJ 



I 



10 



11 



H 



12. 

 11 



