CHAPTER IV 
THE SEGREGATION OF THE GERM CELLS IN 
PORIFERA, CCQELENTERATA, AND VERTEBRATA 
Tue history of the germ cells has not been seriously 
investigated in a number of groups of animals, but, as 
will be demonstrated in Chapters V and VI, there 
are many species belonging to widely separated 
groups in the animal series in which the germ-cell 
cycle is almost as well known as in Miastor. On 
the other hand, the three phyla to be discussed in 
this chapter have been carefully studied for many 
years, but an early segregation of germ cells has not 
yet been established in them to the satisfaction of a 
majority of investigators. It seems strange because 
of the uncertainty of the morphological continuity 
of the germ cells in these animals that one of these 
groups, the C@LENTERATA, should have furnished 
the material upon which Weismann based his elabo- 
ration of the germ-plasm theory. 
1. PoriIrERA 
Sponges reproduce asexually by budding and by 
the formation of gemmules, and sexually by means of 
ova and spermatozoa. Budding occurs in almost all 
sponges. In most cases the buds remain attached 
to the parent (continuous budding); but in some 
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