144 GERM-CELL CYCLE IN ANIMALS 



nucleus with sixteen chromosomes, the " Richtungs- 

 kopulationskern " passes through three divisions, 

 giving rise to eight " doppelkernige Zellen." After 

 the blastoderm is completed, the products of these 

 eight cells lie in the middle line near the dorsal surface 

 of the egg, where the formation of the amnion begins ; 

 the nuclei of these cells are small, and lie embedded 

 in dark staining cytoplasm. Later they are found 

 just beneath the dorsal surface near the point of 

 union of the amnion with the head-fold of the em- 

 bryonic rudiment. They are next located between 

 the epithelium of the mid-intestine and the ectoderm ; 

 from here they migrate into the coelomic cavities, 

 and finally, at the time of hatching, form a " wellen- 

 artigen" strand, the germ-gland, extending through 

 the third, fourth, fifth, and sixth abdominal segments. 

 The fertilized eggs of the bee were also examined 

 by Petrunkewitsch, but no *' Richtungskopulations- 

 kern" was discovered. In these eggs the genital 

 glands arise from mesoderm cells. Doubt was 

 immediately cast on these results, although Weismann 

 (1904, p. 336) vouched for their accuracy. Thus 

 Wheeler (1904) says, " Even in his first paper there is 

 no satisfactory evidence to show that the cells re- 

 garded as derivatives of the polar bodies in the figures 

 on plate 4 are really such, and not dividing cleavage 

 cells or possibly vitellophags. . . . When we take 

 up the second paper we wonder how anybody could 

 regard the figures there presented as even an adum- 

 bration of proof that the testes of the drone are de- 

 veloped from the polar bodies." Dickel (1904) 



