
No. 426.] THE CILIATED SPONGE LARVA. 459 
egg nature to the large ovum-like cells described by Schulze 
and by myself from Euplectella.” Such an hypothetical mother 
cell of an embryo as Ijima suggests in the above excerpt would 
be something so different from an ovum that to class it as such, 
it seems to me, would be to confuse our ideas concerning repro- 
ductive cells. It would rather be analogous to a spore. How- 
ever, both Ijima's observations and my own on the character 
of the smaller groups of archzeocytes and their growth by fusion 
render unwarranted the assumption that any such cell exists, 
that is, as a typical and necessary condition in the development 
of an embryo. That a single cell may occasionally and inci- 
dentally give rise to a gemmule and so to an embryo is, of 
course, a possibility. And thinking over the possibility of such 
a case tends to clear up our ideas as to the nature of the typical 
reproductive archzeocyte which acts in coóperation with others 
to form a new individual. If the hypothetical, exceptional 
archeocyte, which independently produces an embryo, is to 
be looked on as equivalent to a spore, the same view must be 
entertained regarding the typical coóperative archzocyte. In 
the one case we have a single spore producing the individual, 
while in the other case several spores unite, as, for instance, in 
the production of a myxomycete plasmodium (sporangium). 
Into the deeper-lying question as to how fundamental is the 
difference between an ovum and a spore there is no need to 
go. That there are, except in some of the plants, certain great 
and obvious differences no one will deny. 
From a theoretical standpoint further investigations of this 
type of development in the sponges are much to be desired, 
and Professor Ijima’s contribution will scarcely fail to call 
them out. 
UNIVERSITY OF NoRTH CAROLINA, 
December 20, 1901. 
