90 Development of the Ovum. By W. II. Dallinger & J. Drysdale. 
an envelope ; and within the yolk is seen the “ large round germinal 
vesicle and the germinal spot.” The latter vanishes after impregna- 
tion, and the germinal vesicle becomes eccentric — and the next 
thing we are told is that “ the germinal vesicle was no longer in 
the yolk, but instead of it there was a spindle-shaped something ' 
like that seen in Nephelis.” How was the change effected ? What 
were the steps ? The transition is all-important, hut how it hap- 
pened is not worked out ; and it would be, in so important a 
question, a matter of the greatest interest to know how the perfect 
spindle-formed body, with which these observations begin, arose. 
Nothing final can issue in this inquiry until, from first to last, every 
process and every step therein has been consecutively made out. 
(2) The identity of this body with what is known as the 
germinal vesicle is certainly probable, but by no means certain, at 
present. It is certainly true that this supposition derives con- 
siderable support from the fact that Ratzel found that in the ripe 
ova of Tubijex, prior to laying, the spherical germinal vesicle lost 
its spherical shape, elongated, became spindle-shaped with a meri- 
dional striation, and so forth, closely resembling the nuclear spindle 
of Nephelis. But as the process is described by Butschli this would 
involve the necessity that the whole of the germinal vesicle was 
extruded as the “ Richtungsblaschen ” in every case. Against this, 
however, there are irresistible facts ; and in an appendix to the 
volume the author is bound in some sense to admit that there are 
cases where “ a part of the germinal vesicle may remain.” If this 
be so, evidently there is missing a link in the chain of observation. 
Difficulties of an equally complex character present themselves in 
the collation of these researches with those of other distinguished 
embryologists which it would be hopeless even to attempt to con- 
sider here. 
(3) That the expulsion of the “ Richtungsblaschen ” is a result 
of impregnation must also be abandoned. In the text of this 
treatise the author earnestly contends for this point nevertheless ; 
and endeavours to dispel the force of the very definite results of 
(Ellacher, Bischoff, Flemming, and Beneden. But these are points 
that may be settled with comparative ease, and it certainly is true 
that the expulsion of the “ Richtungsblaschen ” may show itself as 
one of the earliest phenomena of development in the unfertilized 
egg. This is now admitted, and in the appendix is allowed by 
Butschli. 
(4) The universal application of the method of development 
seen in Nephelis , although strongly contended for, and carried by 
analogy into the interpretation of the theory advanced in the third 
part of the volume to account for the propagation of Infusoria, can 
only be admitted with the utmost caution. The evidence given by 
the author is by no means perfect. In Cueulanus eleyans, for 
