and Fertilization in the Nematoidea. 187 



even the mature animal itself, in length. Such instances render 

 it not improbable, that under certain circumstances it is not the 

 spermatozoon itself, but only a portion of it, or an emanation 

 from it, that takes part in the penetration. 

 ^Amongst the species in which the penetration of the zoo- 

 spermia into the ovum has been observed, Ascaris mystax has 

 occupied a leading place. It is now necessary that we should 

 examine how far we may attach unconditional credit to the 

 observations of Nelson and Meissner with regard to this pene* 

 tration. 



Two questions force themselves upon us : first, are the cor- 

 puscles, which, according to Nelson and Meissner, effect the 

 fecundation, the true zoospermia ? and, secondly, do these cor- 

 puscles actually penetrate into the e^^ ; or, at least, are the 

 observations of Nelson and Meissner upon their penetration 

 decisive ? 



We have already indicated how we answer the first question. 

 Upon this point we agree perfectly with Nelson and Meissner, 

 and regard the thimble-like corpuscles as true zoospermia. It 

 has already been shown that these corpuscles have nothing to 

 do with the epithelium ; but this by no means proves that they 

 are in any way connected with the act of fecundation. In the 

 elucidation of this question we have derived great advantage from 

 the unfertilized females. All the females of Ascaris mystax that 

 we have investigated were indeed fecundated, as could easily be 

 perceived from the alterations which had taken place in the eggs. 

 On the other hand, we have obtained more than twenty females 

 of Ascaris suilla, in which the eggs did not exhibit the slightest 

 alteration that could be referred to an influence of impregnation, 

 and for this reason we have regarded these females as unferti- 

 lized. There were two females from the Pig, whose ova, to 

 judge from the changes which they had already undergone, were 

 evidently fecundated. It was remarkable that not one of the 

 former Ascarides contained thimble-like corpuscles in their 

 genitalia. In the two latter, on the contrary, the oviduct was 

 closely filled with them. Our friend Dr. de la Valette has ob- 

 served an exactly similar fact in Ascaris mystax. He found a 

 female which, from the condition of the ova, he could not but 

 regard as unimpregnated, and it did not contain a single thimble- 

 like corpuscle. If, on the one hand, we bear these facts in mind, 

 and, on the other, realize the extreme similarity which exists 

 between the last stages of development of the zoospermia in the 

 male sexual organs of Ascaris suilla, and the thimble-like bodies 

 in question, we must be convinced that the latter are the true 

 mature spermatozoa. That the sharply truncated extremity of 

 the finger-like seminal corpuscle of the male acquires a floccu- 



