Development of the Ovum. By W. H ■ Dallinger & J. Drysdale. 89 
and the point of exit of the said vesicle. They are at first entirely 
disconnected, and both, by treatment with acetic acid, prove to be 
true nuclei. But they soon unite in the clear spot or space, and, at 
its expense, rapidly grow. They become a perfect nucleus with a 
distinct envelope and fluid contents, and distributed within the 
latter are dark granules. While these processes have been taking 
place, two of the three segments of the “ Kichtungsblaschen ” have 
again united, and at the same time the transformation of the nucleus 
begins. At two points on opposite sides of the nucleus, and in the 
direction of the long axis of the yolk, there arise clear spots and 
their accompanying rays. Between these, the nucleus differentiates 
itself into long fibres, and becomes a spindle-shaped body exactly 
like the germinal vesicle. An equatorial zone arises in it which 
is called a nuclear band (kernplatte), which now divides ; and each 
half recedes to the opposite ends of the spindle-like body. These 
ends now lose their points and become rounded, and in the mean 
time occurs the furrowing or constriction of the yolk. Another 
equatorial band arises in the nucleus or spindle, and when the con- 
striction of the yolk is half accomplished the formation of nuclei of 
the second generation takes place from the ends of the spindle, 
these being nuclei in the completest sense. These fuse together 
and grow at the expense of the clear space — the growth of the 
nuclei and the diminution of these homogeneous spaces being in all 
cases correlative. When these nuclei are developed, both hemi- 
spheres of the yolk collapse, and an almost spherical shape is again 
resumed. 
What became of the fibres of the spindle was never discovered, 
hut about this time the remaining segments of the “Bichtungs- 
blaschen” reunite, and in it a system of fibres appears. The 
following fission processes are but repetitions of this. 
It becomes from the above apparent that Biitschli takes it for 
granted, first, that the eggs studied had been subject to no earlier 
developmental changes than those with which he starts. Next, 
that there can he no question as to the identity of his “ spindle- 
formed body” and the germinal vesicle. He further at first claimed 
the extrusion of this germinal vesicle as the “ Richtungsblaschen,” 
as a sole result of the stimulus of impregnation ; and ventures to 
consider that the process of nucleus formation described is widely 
diffused in the animal world, and that it is probably universal in 
impregnated eggs. 
But (1) there is not the remotest evidence to show that pro- 
cesses of considerable import may not have preceded the condition 
with which these investigations started ; complex processes are still 
known to occur in the unimpregnated ovum. We have only indeed 
to turn to the next example given by Biitschli himself to prove all 
this. In Cuculanus elegans the ovum leaves the ovarium without 
