of the Sexual Products. 1 6 1 



it was therefore an interesting matter to ascertain whether 

 things went on in the same way in the latter. Unfortunately 

 all the Gasteropoda that I had at my disposal became very 

 opaque at the close of the larval period, and time did not 

 allow me to commence a series of researches upon this point 

 by means of dissections. I was obliged to content myself 

 with ascertaining that the same mode of development occurs 

 in a Heteropod with distinct sexes, the larva? and young of 

 which were frequently met with, namely Atlanta Peronii. 



It is therefore admissible that even those of the Cephalo- 

 phora which have distinct sexes are originally hermaphrodite. 

 However, as my investigations relate only to a single genus, 

 it would be premature to pronounce an opinion upon this 

 point. Even as regards Atlanta , in order to be sure that the 

 two sexes are originally identical, it would be necessary to 

 have proof that some of the young animals that I observed 

 were destined to become males and others females ; and this 

 proof is wanting. 



At any rate the formation of the male sexual products at 

 the expense of the ectoderm, and of the female products at 

 the expense of the entoderm, is ascertained positively in three 

 genera of Cephalophora, belonging to two different orders of 

 that class. 



In the Appendicular ice. I have been unable to follow the 

 primary formation of the sexual organs. But in very young 

 individuals of the genus Fritillaria the ovary was found to 

 be applied against the digestive tube, whilst the testis was 

 contiguous to the posterior extremity of the body. Sub- 

 sequently these two organs came into contact with each other, 

 but without becoming united. However, I only give these 

 facts as a simple indication ; they are too incomplete to prove 

 any thing. 



This confirmation of Van Beneden's views is the more 

 striking, as I was so sceptical when I commenced the exami- 

 nation of the question, and especially because the Cephalo- 

 phora, with their sexual products intimately mixed in their 

 hermaphroditic gland, are precisely the animals in which 

 a priori we should least expect to see these views con- 

 firmed. 



The primary origin of the testis and the ovary in the two 

 primitive lamelhe of the embryo is now ascertained positively 

 in cases taken from two great divisions of the animal king- 

 dom, the Ccelenterata and the Mollusca ; it is rendered very 

 probable by examples taken from the two divisions of the 

 section of the Chordata — namely, the Tunicata and the Verte- 

 brata. 



