THE GERM-PLASM THEORY 297 
differentiated for causing motion and the nerve cells 
for receiving and conducting stimuli. That the germ 
cells remain in a primitive condition during a large 
part of the embryonic period is accounted for by 
the fact that they become functional at a compara- 
tively late stage in ontogeny (Eigenmann, 1896). 
Asexual reproduction by means of fission or budding 
has seemed to some to invalidate the theory of ger- 
minal continuity, but as Montgomery (1906, p. 82) 
has pointed out, “Perhaps in all cases products of 
asexual generation contain germ cells. If this were 
so, it might then be the case that the incapacity 
of any part of the body of an animal to reproduce 
asexually, or even to regenerate, would be due to 
the absence of germ cells in it — but this is merely 
a suggestion.” The probability that the regenerat- 
ing pieces of ccelenterates and the artificial plas- 
modia formed by dissociated sponge cells contain 
germ cells has already been noted (p. 79), but there 
are cases of the regeneration of sex organs that are 
not so easily explained. For example, Janda (1912) 
has found that if the anterior part of the hermaph- 
roditic annelid, Criodrilus lacuum, is removed, a 
new anterior end will regenerate containing both 
ovaries and testes, although not always in their 
normal positions. 
The study of the germ cells in the cestode Moniezia 
expansa convinced Child (1906) that germ cells may 
develop from tissue cells. In this species the germ cells 
are derived from the parenchymal syncytium, which 
has undergone a considerable degree of cytoplasmic 
