158 M. H. Fol on the Primary Origin 



of cells, which results from a hollow or solid invagination of 

 the outer lamella. The ova, on the contrary, descend directly 

 from a certain number of cells of the entoderm. The two 

 organs are sketched out in each of the two sexes ; but the 

 testis is atrophied afterwards in the reproductive individuals 

 of the female colonies and the ovary in those of the male 

 colonies. 



Waldeyer had previously found that the superficial epithe- 

 lium of the ovary of certain Vertebrata is derived from the 

 peritoneal epithelium which covers the middle lamella, which 

 itself appears to be a dependency of the entoderm. The testis 

 is formed at the expense of the Wolfian canal, which appears 

 to be derived from the ectoderm. 



Bringing together his own and these latter results, Van 

 Beneden sees in them a confirmation of his ideas, and con- 

 siders it probable that they will be verified for the animal 

 kingdom in general. It will be admitted that it is going 

 rather quickly to conclude the universality of these phenomena 

 throughout the animal kingdom from two observations so iso- 

 lated, and only one of which, founded upon the investigation 

 of two species of Hydroid polypes, presents the character of 

 scientific certainty ! 



These conclusions must certainly have appeared very bold, 

 to say no more of them, to many readers. Indeed we know 

 that none of the authors who have paid attention to the primary 

 origin of the sexual products in various sections of the animal 

 kingdom, with the exception of the Vertebrata, have observed 

 any facts which could be in accordance with these views. 

 Their generality is so far from being demonstrated, that even 

 among the Ccelenterata there are some of which the sexual 

 products appear to be formed at the expense of the entoderm 

 alone. Hackel is explicit upon this point with regard to the 

 Geryonidas. In Cordyloplwra and in Hydra the sexual pro- 

 ducts are derived from the ectoderm, according to the careful 

 researches of F. E. Schultze and Kleinenberg. Moreover 

 are not the results of the recent investigations in embryogeny 

 of a nature to inspire us with prudential feelings ? Have not 

 very great and quite unexpected differences in the mode of 

 formation of the lamellae and organs been observed even in 

 allied genera? 



Hence it was with absolute scepticism that I, for my part, 

 received M. van Beneden's generalizations. Without throwing 

 the least doubt in the world upon the result of his researches 

 upon two species of Hydroid polypes, I could not admit as pro- 

 bable that this mode of development of the organs of genera- 

 tion was universal, or even very widely diffused. All that I 



