FECUNDATION IN NEMATOIDA. 299 



with the side, sometimes with the closed, and sometimes with the 

 open flocculent end, and were partially imbedded in the egg, but 

 never entirely, as stated by Meissner and Nelson. According to 

 Thompson, the seminal corpuscles probably assist in the softening 

 of the vitellus, but we do not know whether the irregular, and, 

 as it were torn, appearance of the surface of the vitellus depends 

 upon the action (adhesion) of the seminal corpuscles, or whether 

 the latter attach themselves by preference to sections of the 

 vitellus which are naturally uneven. Thompson does not, like 

 Nelson, regard the ragged surface of the egg, and the adhesion 

 of the seminal corpuscles at that point, as unconditionally neces- 

 sary for fertilization, but as partly accidental to a certain extent, 

 and caused by the softness of the surface of the vitellus. The 

 fact advanced by Nelson is established with certainty, that the 

 seminal copuscles come in contact with the eggs of Ascaris, at 

 a time when they possess no true vitelline membrane, and when 

 they have become so soft and delicate, by the reception of a 

 peculiar fluid, that they can take up seminal corpuscles into 

 themselves and unite with them. 



If we sum up what has been said in a few words, it is certainly 

 established that there is a (more or less complete or only partial) 

 penetration of the seminal filaments into the vitellus, but the 

 disputed point round which everything turns is the question 

 whether the egg, at this time, is still destitute of a distinct vitel- 

 line membrane, as the English authors and Bischoff assert, or 

 whether a peculiar membrane with a micropyle exists, as Meissner 

 supposes. 



Now, before taking into consideration the final purpose of the 

 seminal corpuscles, we must go a step backward, in order to 

 glance over the whole history of the development of the seminal 

 corpuscles. Thompson observed this process to take place in 

 Ascaris mystax in the following way : 



The blind extremity of the tubular testis consists of a delicate 

 membrane, in which isolated, elongated granular nuclei are 

 imbedded. In the interior of this part of the testis we see 

 4 — 5 convolutions of a peculiar tube, apparently situated in the 

 interior, which, however, according to Thompson, is a consequence 

 of the action of water. In the blind extremity of the testis, and 

 in the neighbouring parts, there are delicate, nucleated cells of 

 .i/' and T ~" in diameter, and besides these numerous smaller 

 and more simple corpuscles and nucleoli. The smaller cells have 



