and Fertilization in the Nematoidea. 179 



from Dr. Guido Wagener, he has also detected similar structures 

 in various Nematoid worms. 



2. Formation of the Eggs. 



The Nematoidea may be divided into two sections as regards 

 the mode of formation of the eggs. One of these sections in- 

 cludes those species whose eggs are arranged round a central 

 rhachis in the vitellogene ; the other is formed by those species 

 which possess no rhachis. As a general rule, it may be asserted, 

 that all the Nematoidea in which the vitellogene exhibits several 

 eggs in the same transverse section, belong to the first category ; 

 whilst those in which each transverse section only hits upon a 

 single egg, are to be referred to the second. We shall occupy 

 ourselves especially with the species of the first section. Here 

 we again meet with the Ascaris mystaXj at once so celebrated 

 and notorious, and with it the Ascaris suilla. We shall select 

 the latter in preference as the subject of our investigation, as it 

 is better adapted for this purpose than the former. The rhachis 

 is much thicker in it than in A. mystax, and shines through 

 the walls of the organ in the axis of the vitellogene, in the form 

 of a dark column. 



Like Bischofi" and Thompson, we have been unable to find 

 Meissner^s female germ-cells. The germ-stock is full of vesicular 

 elements, which subsequently become the germinal vesicles of the 

 eggs in course of formation. But no appearances which might 

 have been in any way favourable to Meissner's view, were ever 

 observed. It is true that the mode in which the germinal vesicles 

 are first produced could not be ascertained, and we only consider 

 it probable that they increase by division. We think we must 

 contradict Nelson's statement, according to which the germinal 

 spots are first produced, and subsequently surround themselves 

 with a membrane to form the germinal vesicles. 



As the germinal vesicles descend in the genital tube, they 

 surround themselves with a granular substance, the first rudi- 

 ment of the yelk. At the point where this deposit first takes 

 place, the vitellogene properly begins. There is, however, no 

 true boundary between the germ-stock and vitellogene. Even 

 in the so-called germ -stock the germinal vesicles are united to 

 each other by a tenacious transparent substance, which is no- 

 thing but the first commencement of the yelk-deposit. Within 

 this tenacious fundamental substance, small granules gradually 

 make their appearance, — these are the first yelk -granules, which 

 soon become so extremely numerous that it is no longer possible 

 to recognize the germinal vesicle. The contents of the ovarian 

 tube then appear uniformly granular. When the tube is cut 



12* 



