DR. NELSON ON THE REPRODUCTION OF THE ASCARIS MYSTAX. 
585 
tion of the membrane tends no longer to draw it into a single sphere, but into two 
globules ; and thus the division of the yolk is completed. 
This view is further confirmed by the fact, that while the first steps of this process 
take, comparatively speaking, a long time, as soon as the hour-glass form has been 
once acquired, complete division is effected so suddenly that it is invisible ; while a 
violent oscillatory motion is from the same cause communicated to the yolk masses, 
taking some little time to subside. 
The division and movements of the embryonic vesicle, on the contrary, can only be 
ascribed to vitality. 
That this division cannot be produced by the action of the spermatic particles on 
the embryonic vesicle, is evident from the fact, that it does not take place from 
without inwards, but from within outwards. The embryonic spot divides first ; and 
this I have even seen to take place before the germinal vesicle has been ruptured, 
while it was still entire (fig. 65 A-), and consequently long before the seminal fluid 
could possibly exert any influence over its nucleoli, imbedded as they are in the 
substance of the yet solid nucleus (fig. 65 a), surrounded by fluid, and protected by 
the germinal vesicle (fig. 65 b). 
The fissiparous growth of the embryonic spot proves beyond a doubt that its divi- 
sion is caused by vitality inherent in it. 
The embryonic vesicle, although owing its division to the nuclei it encloses, is 
also alive, because it grows in size, and when divided we see it move, not as some 
suppose, by mere electric repulsion ; for I have most distinctly seen it continue to 
revolve in different directions, and in circles of various diameter. 
I am inclined to the belief that these movements of the embryonic vesicles are 
caused by vibratile cilia, from a certain amount of commotion among the yolk 
granules immediately surrounding the vesicle, observable only when the latter is in 
motion. 
But the embryonic vesicle and spot are nothing else than the nucleus and nucleolus 
of the germinal vesicle. Is this, then, alive ? Yes : because, when first thrown off by 
the ovary as a germinal particle (Plate XXVII. fig. 39 c), it is solid ; the external layer 
of which by growth forms a vesicle (fig. 39 d), while the interior remains solid some 
time longer, and constitutes its nucleus (fig. 39/’). 
This nucleus has been already shown to possess vitality, and as it exists in the 
germinal particle, it also must be alive. 
The growth of the germinal vesicle, therefore, from the germinal particle, is as 
vital as the growth of the embryonic vesicle from its nucleus, the germinal spot. 
We have seen that life does not originate at the period of fecundation ; we have 
traced the vitality possessed by the ovum as far back as the very commencement of 
the ovule ; we must therefore admit that it is derived from the mother. 
For as the germinal particle is living when thrown off by the ovary, and as the 
