242 A Sketch of Comparative Embryology. [ April; 
the kinds of which, like the varieties of mass-motion, are deter- 
mined through localized imbibition. On this account, and be- 
cause the motor acts have laid out the paths of growth, the paral- 
lelism between the series of morphological processes and of the 
motor processes is strikingly complete; but a presentation of these 
details, in the same order, must remain for the future. 
d 
:0:—— 
A SKETCH OF COMPARATIVE EMBRYOLOGY. 
BY CHARLES SEDGWICK MINOT. 
Il.—THE FERTILIZATION OF THE OVUM. 
N the previous article we traced the relation of the genoblasts, 
or sexual products, to the cells from which they arise. We 
have now to consider the manner in which these products effect 
the creation of a new and complete animal. Now, the bodies of 
all animals are composed of cells and the productions of cells, 
hence to make an animal the first thing is to furnish cells. Ac- 
cording to the theory propounded in the last article, an egg rep- 
resents one part, a spermatozoon another part of a cell, hence a 
fusion of the two would again make a single perfect cell. This 
fusion actually occurs, and is called the impregnation or fertiliza- 
tion of the ovum. 
Our knowledge of this phenomenon is extremely imperfect. 
It has, however, been the object of several important researches 
during the last few years, but we must wait for much more 
extended investigations before we can make any satisfactory gen- 
eralizations. The following order of events is that which our 
present knowledge renders most probable—it must be remem- 
bered that we are dealing only with a probability. A single 
spermatozoon enters the egg and fuses with it. After the ejec- 
tion of the polar globules, the dares o the egg isa small body 
which lies near the periphery, i th the globules. 
It then is called the female pronucleus, and tavelocowhy or how 
is not known—towards the center of the egg, where it finally 
remains. A system of radiating lines runs out from it into the 
yolk, making, together with the LOTRE the so-called female 
. BUT. 
