DEVELOPMENT OF THE GENERATIVE ORGANS. 717 
Although no axiom in physiology is now better supported 
than Virchow’s aphorism, even Stricker, in 1870, said, ‘ The 
formation of fresh nuclei within cells must be admitted to pro- 
ceed not only from the fission of old nuclei but from the growth 
of entirely new ones.’ Such a belief is, however, now entirely 
superseded, as the observations of Volkmann and Steudener, 
Metschnikoff, and others have repeatedly shown that such 
appearances are entirely deceptive, and due to the invasion of 
leucocytes, whilst the researches of Flemming, Strasburger, and 
others have placed the question of nuclear division upon an 
entirely new footing. Nevertheless, writers on the embryology 
of Insects are very prone to return to views which are substan- 
tially the same as those originally held by Schwann, and to 
adopt the hypothesis that nuclei may originate in a blastema, 
whilst others maintain that nuclei may be developed from pre- 
existing nuclei, and exist as such in a blastema, or formative 
material foreign to that of the cell in which they are formed, 
and that new cells are developed by the aggregation of this 
material around such originally naked nuclei. Thus Brandt, in 
1878 [330], said a general investigation of the manner in which 
the blastoderm is formed, in Insects, is not unnecessary at the 
present time, as several conflicting views are held which 
culminate in two extremes; according to one of these the 
cells of the blastoderm arise spontaneously in a peculiar 
peripheral layer of the yelk—the yelk blastema; according 
to the other, the cell-substance only is derived from this 
layer, and the nuclei arise from the division of the germinal 
vesicle. 
The result of Brandt’s investigations were the following con- 
clusions: the germinal vesicle does not disappear in the yelk, 
but is itself a cell—in other words, a germ-cell, the nucleus of 
which is the true germinal vesicle—that the division of this 
germ-ovum gives rise to the cells from which the blastoderm is 
developed. 
So far Brandt, therefore, arrived at the same conclusion as 
myself; but there is this difference, Brandt apparently believed 
that the products of the segmentation of the germ-ovum are 
