160 M. H. Fol on the Primary Origin 



rapid development ; it is this circumstance that previously 

 prevented my recognizing it in the organ of large dimensions 

 which it has become in individuals but little larger than the 

 preceding ones. It then presents the form of a thick elongated 

 body, tabulated on its surface, and surrounding the base of 

 the nutritive sac like a half-cylinder. The spermatozoids 

 speedily form in the lobules of this organ ; it is the testis. 



It remained to discover the primary origin of the pyriform 

 body of J. Mtiller. The youngest larvae of Creseis that I met 

 with already possessed it. It was globular and very small, com- 

 posed of a few cells, and situated near the anus. Sarcodic 

 filaments attached it to the anus and the neighbouring part of 

 the ectoderm. It is well known that most of the larva? of 

 the Cephalophora possess by the side of the anus two cellular 

 masses which project into the cavity of the body, and originate 

 by proliferation from the ectoderm of the anal region. One 

 of these cellular bodies gives origin to the kidney. The other 

 some authors regard as the origin of the genital organs — an 

 opinion which is not founded upon any positive observation, 

 but only on the fact that they did not know what other signi- 

 fication to attribute to it. This cellular body is no doubt the 

 origin of the pyriform body, which is nothing but the rudi- 

 ment of the testis. The testis, therefore, originates from the 

 ectoderm. 



The ovary is formed in the manner that I have described 

 in my memoir on the Pteropoda. The only error into which 

 I have fallen with regard to it has been that I have taken the 

 rudiment of the ovary for the origin of the entire herma- 

 phroditic gland. Each of the brownish cells, a single layer 

 of which composes the wall of the nutritive sac, divides cross- 

 wise into an exterior transparent cell and an interior brown 

 cell. This scission takes place only on the right side of the 

 sac. The inner layer of brown cells continues to form the 

 epithelium of the nutritive sac, whilst the exterior layer 

 envelops it in the form of a half-cylinder. The cells of the 

 latter layer multiply slowly, then begin to enlarge ; and each 

 of them becomes an ovule. But these ovules do not attain 

 their maturity until after the more or less complete evacuation 

 of the semen accumulated in the testis. 



I have ascertained the same facts in an orthoconchal Ptero- 

 pod, Styliola subulata. 



In Creseis the male and female parts of the hermaphroditic 

 gland are simply applied to each other throughout their length, 

 and their contact does not become intimate until after the 

 absorption of the nutritive sac. But the ovary and the testis 

 do not mingle so intimately as in the other Cephalophora ; 



