DEVELOPMENT OF THE GENERATIVE ORGANS. 713 
a distinct membrane.’ This phenomenon was regarded by 
Weismann as exceptional, and probably due to the accidental 
non-fertilization of the eggs. 
Metschnikow [841] says that he failed to discover a germinal 
vesicle in Insects’ eggs, and Ganin [848] states that in all the 
Ichneumonidae which he examined the germinal vesicle dis- 
appears at a very early period of egg-formation, before the 
mother organism escapes from the pupa. 
Stuhlmann [863], like Brandt, believes that the ovarian 
egg in the Blow-fly is developed from a single cell, and that 
the so-called nutrient cells undergo atrophy and remain outside 
the chorion. He regards the nucleus of this cell as the 
germinal vesicle, and says, ‘I have been enabled, by a large 
nurnber of observations on Insects’ eggs, to establish the extru- 
sion of nuclear particles from the germinal vesicle, which are 
afterwards lost in the egg-plasma. Later the germinal vesicle 
disappears, until at last we find it again at the upper egg-pole 
as a segmentation nucleus. The ‘outstreaming of nuclear 
particles,’ described by Stuhlmann, is quite unlike the extrusion 
of the polar globules in other ova. It undoubtedly occurs from 
all the nuclei of the yelk-cells and also from those of the various 
larval organs during their degeneration in the pupa. It is a 
phenomenon characteristic of the histolysis of the tissues and 
the breaking up of the nuclei of effete cells. 
Lastly, the identity of the first segmentation nucleus with the 
nucleus of the egg-cell is assumed by Stuhlmann, and not proved, 
as the disappearance of one structure and the subsequent 
appearance of another cannot establish a genetic connection 
between them. 
Henking [850], like his predecessors, has attempted the 
identification of a germinal vesicle in the egg of the Blow-fly. 
He says, ‘The unripe egg contains a germinal vesicle and 
germinal spot. The former is clear and does not stain deeply 
with borax carmine.’ In some of my sections I have found 
one or even two yelk nuclei, which resemble Henking’s germinal 
vesicle, but the same nuclei in the next section in the series 
exhibit characters which are indistinguishable from those of 
