136 ZOOLOGY 



no account could be given of their detailed behaviour. No 

 distinctive leptotene and early diplotene stages could be made 

 out, but the chromosomes became distinct again in the metaphase 

 of the heterotype division. They are, however, irregular in out- 

 line, and no flat metaphase plates could be found except in 

 D. ohscura and closely related species. The distribution of the 

 chromatic material, however, is perfectly regular. The second 

 division is much more normal and presents no special peculiarities. 

 Metz observes may interesting cytoplasmic structures but does 

 not analyse them. These structures are believed to be the so- 

 called scattered chromosomes of Jeffrey and Hicks. Comparison 

 on an accurate basis is, however, impossible, as the two latter 

 workers use Carnoy's solution for " fixation." This fixative, 

 although a good penetrant of chitin and fatty tissue, is not good 

 cytologically. 



There is little doubt that this description of Metz requires 

 confirmation, and much that may be interesting from a theoretical 

 point of view would probably result. 



Turning to the nucleolus we find that a considerable amount of 

 attention has been given to this organ from various aspects. For 

 instance in 1920, Hogben described processes of nucleolar emission 

 of granules in Hymenoptera (55), Periplaneta (56) and Libellula (57). 

 This was done primarily with the view of sustaining the indivi- 

 duality and continuity of the chromosomal material throughout 

 the germ-cell cycle. It also had another significance, for, as 

 pointed out by Hogben in the case of Periplaneta and Libellula, 

 these emissions are apparently connected with vitello-genesis. 



In the case of the Hymenoptera studied by him (Synergus and 

 Formica rufa) nuclear particles were ejected as the germinal 

 vesicle became lightly staining. They migrated to the cytoplasm, 

 fragmented and acquired an enclosing membrane. They 

 were, however, transitory in nature. In Periplaneta the 

 process is more complicated. During the earlier stages of the 

 oocyte, particles are emitted from the nucleolus, or plasmosome, 



