108 M. Oscar von Grimm on the Agamic Reproduction 



view, I was so fortunate a few days ago as to detect, quite 

 unexpectedly, what I had so long sought in vain. I laid the 

 abdomen of a pupa containing well-formed ova in glycerine, 

 and in the course of a few days, when I remembered this pre- 

 paration, I examined the ova under the microscope. My de- 

 light may be imagined when I saw very distinctly the ger- 

 minal vesicle in a series of ova (fig. 12, gv), and with them 

 an ovum with the germinal vesicle engaged in division. 

 The germinal vesicle was 0"045 millim. in diameter. Its 

 division takes place in a direction transverse to the ovum. 

 These two objects seem to prove prefectly that the germinal 

 vesicle by no means disappears, but by dividing becomes con- 

 verted into the germ-nuclei. But the circumstance that so 

 many admirable observers (as Weismann, for instance) could 

 not find it, and thought themselves compelled to assume a free 

 formation of the germ-nuclei, was probably caused by the opa- 

 city of the yelk, and the difficulty of investigation dependent 

 thereupon. 



We may now therefore assume that the union between the 

 germ-nuclei and the germinal vesicle, and also between the 

 different generations, actually exists, and therefore that omnis 

 ceUula e celhda. 



The first alteration in the deposited ovum consists in the 

 contraction of the contents in the direction of the longitudinal 

 axis of the ovum. In consequence of this contraction a polar 

 space is formed in each end of the ovum, of which the lower 

 one, or that in the caudal pole, is larger than the opposite one. 



We then observe an alteration in the periphery of the yelk : 

 there is formed here a homogeneous, limpid blastema-layer, 

 the so-called blastema of the blastoderm {Keimhautblastem , 

 Weism.), Avliich appears to be thickest in the region of the 

 inferior pole of the ovum. This blastema is nothing but a 

 homogeneous mass, which has separated from the yelk ; it is 

 therefore a part of the vitellus, and may probably be regarded 

 as the formative vitellus of insects, whilst the yelk enclosed in 

 this functions as the nutritive vitellus. Soon after the sepa- 

 ration of the formative vitellus a germ-nucleus makes its 

 appearance in the inferior pole of the ovum, and, sm-rounded 

 by a portion of the formative vitellus, passes as the so-called 

 polar cell into the inferior polar space ; here the mcmbrancless 

 cell divides into two cells, each ot which again divides, so that 

 we finally obtain four polar cells. Frequently, however, the 

 nucleus of the first polar cell divides while still lying in the 

 layer of formative vitellus, so that two polar cells appear at 

 once in the polar space. During the appearance of the first 

 polar cell we see many germ-nuclei, formed by the division of 



