B. F. Kingsbury 115 



the idiozome which becomes the center of radiations extending through- 

 out the cell-body and also penetrating the idiozome itself, Fig. 9. 

 "When the centrosomes have moved apart, a delicate spindle may be 

 seen extending between them. This spindle increases in size as the 

 centrosomes move farther apart, and with the dissolution of the nuclear 

 membrane, which occurs when the spindle is about half grown, pene- 

 trates the nucleus, some of the fibers becoming apparently attached to 

 the chromosome rings as the mantle fibers. When the spindle is first 

 formed its axis may make any angle with the nuclear membrane. Figs. 

 9, 10; but as it increases in size, it seems to rotate so that the axis is 

 roughly tangential to the nuclear membrane. In some cases the spindle 

 could be observed before the outline of the idiozome had disappeared, 

 Fig. 10. This, together with the penetration of the idiozome by the 

 radiations are features not observed in the other Amphibia, Moves find- 

 ing in Salamandra that the centrosphere fragments took no part in the 

 formation of the spindle. In Desmognathus, this does not seem to be 

 the case. The chromosome loops do not seem to retreat to the opposite 

 side of the nucleus, but rather to collect upon the side next the spindle. 



The linin of the nucleus, I am sure, takes no part in the formation 

 of the spindle, but has a different, irregailar appearance, as of degenera- 

 tion, and stains somewhat differently. 



The chromosomes, at the stage when they are drawn upon the spindle, 

 are irregular rings, usually much distorted; occasionally presenting the 

 form of a Y, by partial fusion of the sides. The typical stage of the 

 spindle formation, such as is shown in Meves' figure, in which the chrom- 

 atin rings bend in response to the attachment of the mantle fibers to 

 the ends, are of rarer occurrence in Desmognathus, Fig. 13. The 

 methods employed did not reveal any difference between mantle fibers 

 .and central fibers, nor from the study of this division in Desmognathus 

 did there appear to be sufficient evidence for the conclusion that the 

 arrangement of the chromosomes on the spindle and their subsequent 

 migration are due to the mechanical force of contraction in the mantle 

 fibers. A careful study of the mechanics of mitosis in the spermatocyte 

 has not been attempted, hoAvever. 



The succeeding stages in the mitosis of the spermatocyte of the first 

 order have been carefully described by Meves, Flemming and McGregor, 

 and Desmognathus diff'ers from the forms investigated by them only in 

 apparently unimportant details. The spindle varies in shape and size 

 though the volume of the spindle appears to remain nearly constant, the 

 shorter spindles being broader. In Desmognathus, as in the other forms, 

 the chromosomes vary in shape and actual size. The amount of fusion 

 10 



