114 The Spermatogenesis of Desmognathus Fusca 



fixed in Platino-aceto-osmic mixture, and may be due to the precipitation 

 of proteids dissolved out when the latter fluid is used, which suggests 

 that the idiozome acts as the nutritive center of the cell. 



The two points which seem to need emphasis in discussing this stage 

 of the spermatogenesis of Desmognathus are: (1) the early establishment 

 of definite chromosomes while growth is still taking place, and (2) their 

 polar orientation during tbis period of growth in relation to the idio- 

 zome and centrosomes. The early formation of the chromosomes in 

 other Amphibia does not seem to have been very definitely recognized 

 or noted, save in the case of Batrachoseps by Eisen. 



The First Division. — The first indication of the division of the 

 spermatocyte occurs in the change of position of the chromosomes. 

 They lose the polar arrangement which they have maintained through- 

 out their period of growth and possess no recognizable arrangement in 

 relation to the idiozome. They do, however, exhibit a tendency to take 

 up a superficial position beneath the nuclear membrane. The splitting 

 of the chromatin threads follows next in close succession. Fig. 6. The 

 details of the splitting are difficult to determine. The chromatin seg- 

 ments are long and still possess a bead-like structure. In them the 

 splitting appears as a succession of clefts originating (in some cases at 

 least) in the less chromatic part and merging at last in one continuous 

 space. In which case, it would seem that the division did not begin 

 with the chromatin granules. Whether or not the splitting is com- 

 plete and the daughter-threads are at first separated throughout their 

 entire length and afterwards fuse at their ends, could not be satisfac- 

 torily determined. Moves, 96, believed this was the case in Salamandra, 

 and it seemed to be the case in Desmognathus as well, though it was 

 hard to determine whether or not the ends seen in a section were free 

 or cut ends. The point, however, is a minor one on our present basis of 

 'knowledge, and need not be considered further. The splitting is fol- 

 lowed by a thickening and shortening of the double chromosomes which 

 now are seen to be fused at their ends. In this stage they are usually 

 distorted and twisted, assuming a variety of shapes. Figs. 7, 10. They 

 may be twisted once, presenting the figure of an 8; they may be twisted 

 twice; and also twisted and bent. The typical ring, 0, is frequently 

 found but by no means constantly, even in stages approaching the 

 establishment of the equatorial plate stage. 



The splitting of the chromosomes takes place before there is any 

 perceptible change in the idiozome or the centrosomes. The latter 

 become larger, Figs. 6, 8, 9, stain more intensely and are of vaguer out- 

 line, appearing surrounded by an umbra. They migrate apart within 



