of the Unfertilized Egg in certain Sawflies (Tenthredinidae). 105 



some number in the mitoses of the yolk-nuclei derived from the 

 egg-nucleus remained the same as in the maturation divisions, 

 this has been confirmed by other sections of this species, and is 

 seen even more clearly in P. luteolum, where the chromosome 

 number is clearly eight, both in the polar mitoses and in those 

 found in the blastoderm. This raises an important question, for P. 

 luteolum, can continue to reproduce parthenogenetically for several 

 generations, and if no doubling of the number takes place it 

 seems impossible that reduction can occur. The question cannot 

 be settled definitely until the oogenesis or spermatogenesis is 

 worked out, but my provisional conclusion is that both maturation 

 divisions are equational, and that no reduction takes place. 



Another point of interest concerns the centrosome. In none 

 of the species studied have I been able to find centrosomes in the 

 polar mitoses, but in the divisions of the yolk-nuclei and in the 

 blastoderm they are conspicuous, consisting of a central deeply 

 stained granule surrounded by a clear field. Since the eggs are 

 unfertilized they cannot be derived from the spermatozoon, and it 

 seems certain therefore that they arise de novo, as was found by 

 Wilson in artificially parthenogenetic eggs of Echinoderms. 



8—2 



