294 THE OVARIAN EGG. 
time produce broods at fixed intcrvals; while 
others, again, reach their mature state very rap- 
idly, and produce a number of successive genera- 
tions in a comparatively short time, it may be 
in a single season. 
I do not intend to enter upon the chapter of 
special differences of development among ani- 
mals, for in this article I have aimed only at 
showing that the egg lives, that it is itself the 
young animal, and that the vital principle is active 
in it from the earliest period of its existence. But 
I would say to all young students of Embryology 
that their next aim should be to study those in- 
termediate phases in the life of a young animal, 
when, having already acquired independent exist- 
ence, it has not yet reached the condition of the 
adult. Here lies an inexhaustible mine of valu- 
able information unappropriated, from which, as 
my limited experience has already taught me, 
may be gathered the evidence for the solution of 
the most perplexing problems of our science. 
Here we shall find the true tests by which to de- 
termine the various kinds and different degrees 
of affinity which animals now living bear not 
only to one another, but also to those that have 
preccded them in past geological times. Here we 
shall find not a material connection by which 
blind laws of matter have evolved the whole 
creation out of a single germ, but the clew to that 
