714 THE GENERATIVE ORGANS. 
the other yelk-cells. Henking further claims to have discovered 
the rudiment of a germinal vesicle in ripe eggs and to have 
traced the first segmentation spindles. As the latter could 
only occur after impregnation, the important question in rela- 
tion to the views I have expressed is, whether a germinal 
vesicle really exists in the unripe ovarian eggs, and on this 
point Henking’s results appear to me to be no more satisfactory 
than those of his predecessors. I cannot admit that there is 
any evidence that his germinal vesicle differs from the nuclei 
of the other yelk-cells. 
The changes which occur in the germinal vesicle previously 
to fertilisation are now very well known in many Invertebrates, 
Echinoderms, Ascaris, etc., and have also been observed in 
some Vertebrates, as in the Rabbit, so that there is no doubt 
these phenomena are of very general and probably universal 
occurrence. 
Either before, or immediately after, the ovum is discharged 
from the ovary it undergoes changes preparatory to, but 
entirely independent of, fertilisation. The germinal vesicle 
approaches the surface of the vitellus, loses its distinctness of 
outline and after exhibiting karyokinetic changes which are 
characteristic of a nucleus about to divide, first one and then 
a second portion separates and is extruded from the yelk. The 
two minute bodies which are extruded from the yelk are known 
as polar bodies or directive corpuscles. The remainder of 
the nucleus, which remains within the yelk, is termed the 
female pronucleus. 
The Polar Bodies or Directive Corpuscles are not to be con- 
founded with the polar globules of Weismann. They are 
developed before, and not after, impregnation. Weismann’s polar 
globules are nucleated cells, and their appearance is contempo- 
raneous with the formation of the blastoderm. They are pre- 
cisely similar to segmentation spheres. It is unfortunate that 
two structures so entirely different should have received similar 
names, but the term polar globule was used by Weismann 
before directive corpuscles were known. 
The Formation of Directive Corpuscles in Insects.—Robin [360] 
