142 T. H. MONTGOMERY, JR. 



chromosome, but the width of this split never becomes wider 

 than that shown in Fig. 1 1 . Janssens and Dumez, as all the 

 workers on amphibian spermatogenesis before them, have entirely 

 overlooked this split of each arm of a bivalent chromosome. 

 With material stained in iron haematoxyline, and sufficiently 

 destained, this split, though narrow, is perfectly distinct. 



There is a point brought up by Janssens and Dumez to which 

 attention must be drawn. They maintain (i) that there is no 

 regular occurrence of a band of linin (that marked k in the figures 

 of my previous paper), joining the two univalent arms composing 

 a U, and placed at the bend of the U ; and (2) that the linin 

 spirem appears continuous and not broken into as many segments 

 as there are U-shaped loops. A reexamination shows me that 

 they are right in regard to there being here a continuous linin 

 spirem. And this is exactly what I gave especial study to 

 proving to be the case in the corresponding stages of Pcripatns. 

 But I must maintain against these writers, that in Plethodon and 

 Desmognathus, as in Peripatus, there is at no stage in the sper- 

 matocytes a continuous chromatin spirem. Sometimes one arm 

 of a U-shaped chromosome seems to be continuous with the end 

 of an arm of another, as in Fig. 1 1 (and Fig. 5 of my preceding 

 paper). But this is unusual, and generally one finds, as in Figs. 

 8, 10 and 11, that the ends of the U-shaped chromatin loops are 

 connected with the ends of other loops only by linin. Hence 

 the boundaries of the bivalent chromosomes are perfectly distin- 

 guishable in most cases. As to the first point, I admit that the 

 U-shaped loop, which I regard as composed of two univalent 

 chromosomes attached at the bend of the U, does not show in all 

 cases a band of linin at its bend ; but it does nevertheless in many 

 cases. However, on this point I did not place great insistence, 

 as Janssens and Dumez maintain. 



The U-shaped bivalent chromosomes of Fig. 1 1 shorten and 

 condense into forms such as shown in Fig. 12. By the conden- 

 sation of the chromatin the longitudinal split becomes hidden. 

 This is not a remarkable phenomenon, as maintained by the 

 Belgian writers ; I and others have described it for frequent 

 cases in arthropods. It reappears in the anaphase of the first 

 maturation mitosis as a split along which the chromosomes 



