720 THE GENERATIVE ORGANS. 
is necessary for the comprehension of the other. Van Beneden 
and Julin [867], 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 Hertwig is 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 [844]: ‘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 
mass. This phenomenon occurs in the greater number of 
Trematodes, Cestodes, and in certain Turbellarians, such as 
the Planarians and Nemertids, in some Nematodes, and in the 
greater number of Crustacea.’ 
