4 H E WITT, Cytologkal A sped of PartJienogenesis in Insects. 



HYMENOPTERA. 

 Apid^. 



Apis mellifica. An excellent account of the progress 

 of our knowledge of the parthenogenesis of this insect and 

 the theories connected with it is given by Phillips (78). 



Blochmann (11) first described the polar bodies of the 

 drone-egg. Petrunkewitsch (74) has studied the changes 

 which take place in the maturation of the drone-egg, and 

 in a later paper (75) he gives an account of his investiga- 

 tions as to the fate of the polar nuclei. 



The nucleus of the ovum approaches the periphery 

 of the egg. Here it undergoes two successive divisions 

 {Fig. 8). In this manner four nuclear masses, groups of 

 chromosomes, are formed. Of these the two outer portions 

 are the halves of the first polar nucleus, and the two 

 inner are the second polar nucleus and the female pro- 

 nucleus. Each nuclear mass contains eight chromosomes, 

 the original nucleus having contained sixteen. The inner 

 half of the first polar nucleus and the second polar nucleus 

 fuse (/^/o-.9),and form a single nucleus (j-) containing sixteen 

 chromosomes. Petrunkewitsch terms this the " copulation- 

 nucleus," an unfortunate term in my opinion, and I propose 

 to call it the Syntelosovie. The outer half of the first polar 

 nucleus wanders outwards, becomes flattened against 

 the periphery and degenerates ; the female pronucleus 

 migrates inwards {Fig. 10). 



Petrunkewitsch has followed the syntelosome, and 

 finds that it gives rise to the germ cells of the male, by 

 subsequent divisions in the dorsal region of the embryo. 

 The cells thus formed being the primordial germ cells 

 forming the spermatogonia. As these arise from the 



