114 bulletin: museum of comparative zoology. 



Blackman ('05) found a plasmosome attached to the accessory chro- 

 mosome of Scolopendra. A long Hst might be added to show that 

 plasmosomes have been found associated with particular chromosomes. 

 Many attempts, not altogether successful, have been made to explain 

 the baffling relations to the other cell-structures of such bodies as have 

 been called plasmosomes, nucleoli, chromoplasts, karyospheres, etc., 

 but any future attempts to elucidate these relations must, I believe, 

 be accompanied by a recognition of the relations that these structures 

 bear to the organization of individual chromosomes. 



4. Persistence of chromosomes between mitoses. It still remains to 

 discuss what may be the nature of the "organization" of the chromo- 

 somes in the stages through which the nuclear substance passes from 

 one metakinesis to the next. I shall consider briefly (1) the origin of 

 the nucleus from the chromosomes, and (2) theories of continuity. 



(1) Origin of the nucleus. In my description of the spermato- 

 gonial divisions of Phr\Tiotettix (p. 87-91), I pointed out that each 

 chi-omosome becomes surrounded, as early as the anaphase, by a 

 hyaline region, that this region expands in the telophase; that the 

 chromatin of each chromosome becomes diffused to a certain extent 

 within its own region; that a membrane becomes formed at the 

 boundary between the hyaline region and the cytoplasm, producing 

 the chromosomic "vesicle"; and that the nuclear membrane consists 

 of the outer walls of the vesicles at the periphery of the nuclear group. 

 I drew the conclusion that the hyaline region was formed at the ex- 

 pense of the cytoplasm and that the material of each chromosome 

 tended to remain within the space of its own vesicle, a core of chroma- 

 tin being particularly noticeable in the center of this region, and that 

 the prophase chromosome subsequently formed was developed out of 

 the substance of one, and only one, of the previously existing telophase 

 chromosomes. Sutton ('00) was the first to describe the vesicles of 

 the spermatogonia of a grasshopper. Since then, Otte ('07) has seen 

 similar structures in Locusta, and Davis ('08) in several Acrididae; 

 Pinney ('08) has described them for Plirynotettix. Sutton stated 

 that in the earlier stages of nuclear formation, each chromosome 

 produced a separate vesicle, just as I have found for Plirynotettix, 

 but that in later stages, the proximal ends fused together, giving a 

 common nuclear cavity, from which the distal ends of the vesicles, 

 particularly the longer ones, projected out like the fingers of a glove. 

 Sutton interpreted these conditions as lending strong support to the 

 theory of individuality. Otte believed that the individual vesicles 

 remain distinct throughout the whole of the interkinetic phases, and 



