7 2o THE GENERATIVE ORGANS. 



is necessary for the comprehension of the other. Van Beneden 

 and Julin [367], with a correct appreciation of this fact, followed 

 out their investigations on the development of the sperma- 

 tozoa in Ascaris megalocephala ; and more recently the litera- 

 ture of the subject has been enriched by many partial 

 investigations, and some very suggestive studies amongst 

 nematoid worms.' 



The subject is one which is so complex, and which bristles 

 with so many contradictory statements, that I cannot enter 

 further upon it ; that in the main the view of Hertwigis correct, 

 appears to me indubitable, but those who wish for further in- 

 formation are referred to the memoirs, a list of which is given on 

 page 712, and to the extensive bibliographies which they contain. 



The Development of Germ-Ova in various Animals. The manner 

 in which germ-ova originate in Worms and Crustaceans has 

 been frequently studied, and does not appear to differ mate- 

 rially from the process as it occurs in the Mammalia. 



Van Beneden wrote [344] : ' One may say that in all the 

 Worms, Crustacea, and even in the Vertebrates, the first 

 rudiments of the egg are formed in the same manner. It is 

 probable that it is the same in all the members of the animal 

 kingdom. 



' The first rudiments of the egg, the germs, are formed at the 

 expense of a common layer of protoplasm, holding in suspen- 

 sion distinct nuclei. When these nuclei have attained a cer- 

 tain volume the protoplasm aggregates itself around them in 

 a distinct layer, and from this moment the germs consist of 

 the essential parts of a cell. 



' It is incontestable that in certain cases this phenomenon 

 is accomplished by the formation of furrows, which extend 

 inwards from the surface. 



' In other cases the protoplasm appears to become more 

 dense around the nuclei, and separates from the common 

 ii. ass. This phenomenon occurs in the greater number of 

 Trcmatcdcs, Cestodes, and in certain Turbellarians, such as 

 tin- Flanarians and Nemcrtids, in some Ncmatodes, and in the 

 greater number of Crustacea.' 



