SPERMATOGENESIS OF SCUTIGERA FORCEPS. 165 



ules composing them become fused closely together, and from 

 now on the chromosome always appears as a single structure 

 (Fig. 13 ct scq.\ The enveloping sheath likewise continues to 

 draw more closely about it, until it is finally indistinguishable 

 from its contents (Fig. 15). By the time the last chromosome 

 emerges from the karyosphere, those issuing first have already 

 begun to undergo this operation ; but, since each assumes the 

 tetrad form very quickly after making its appearance in the nuc- 

 lear area, presently all seem to be in an equally advanced stage 

 of development (Figs. 12, 13, 15). 



The history of the centrosome is one of the most difficult 

 questions in the study of spermatogenesis of Scutigcra forceps, 

 on account of the peculiar nature of the cytoplasm. In struc- 

 ture this consists of an exceedingly fine and regular net-work, 

 staining brownish with the iron-haematoxylin. A further diffi- 

 culty is due to the presence in the cytoplasm of small bodies, 

 probably of the same nature as the larger bodies mentioned 

 above. These particles are indistinguishable from the centro- 

 somes, except when the latter may be indicated with certainty by 

 the surrounding astral rays ; but these rays offer no sure solu- 

 tion of the problem, for they are of an extremely delicate nature, 

 and endure for only a brief period. Carnoy encountered the 

 same difficulty in Scutigcra arachnoides, of which he says : " Les 

 figures caryocinetiques y sont plus deliees et moins demonstra- 

 tives " than in Lithobius forficatus, which he has already described 

 as being hard to study on account of its having such dense and 

 opaque cytoplasm. 



Because of these difficulties, the centrosomes cannot be dis- 

 tinguished with certainty until the opening of mitotic activity. 

 In the early prophase (Fig. 12), a pair of minute granules may 

 be observed, situated in the cytoplasm at each side of the nuc- 

 leus, about one third of the distance between its membrane and 

 the cell-wall. These lie in a transparent clear space from which 

 astral rays of exceeding delicacy extend out for a short distance 

 into the cytoplasm, where they gradually become lost in the 

 net-work. During the breaking down of the karyosphere and 

 the formation of tetrads, these centrosomes remain stationary in 

 the cytoplasm, and the asters maintain a nearly uniform size and 

 strength. 



