FORMATION OF THE FIRST SPERMATOCYTE CHROMOSOMES 577 



as I know, gives the first example in which both methods are 

 found in the same individual. 



As previously stated, the doubly split chromatin threads 

 remain throughout at least the greater part of the growth period 

 (plate 1, fig. 1). I have not been able clearly to follow the pair- 

 ing of the chromosomes in synapsis, and cannot say whether the 

 two parts of the split thread are maternal and paternal elements 

 which have conjugated side by side or whether the split is a 

 division of single chromosomes which have united end to end. 

 In such rings as figures 10 and 11, plate 1, there is no indication 

 of the point where the two chromosomes join. Perhaps it appears 

 later, but then the rings become lost among the others and it 

 is impossible to trace them. In the early prophases, some of 

 these threads open out, forming rings as shown in figures 2 to 11, 

 plate 1. I have studied this point very carefully, being some- 

 what reluctant to believe that both methods could be present 

 in the same species, but after going over the slides again and 

 again, I have become convinced that such is the case. Plate 1, 

 12 to 17, shows various stages in the bending and twisting of 

 these threads as they open out into rings. 



Ring formation by bending is much clearer and here I have 

 been able to trace the process in a number of different chro- 

 mosomes. By careful study it is possible to recognize individually 

 some of the chromosomes during this process of ring formation. 

 This makes it possible to trace practically every step in the 

 process and I have figured a complete series in the case of four 

 chromosomes. Plate 1, figure 18, shows one of these chromosomes 

 which can be distinguished by its shape and size. Figures 19 to 

 21 show clearly the formation of the ring by bending, while 

 figures 22, 23 and 24 show the steps in the transformation into 

 the chromosome of the first spermatocyte. By this series it is 

 clearly seen that the composition of the bivalent chromosome (24) 

 is the same as if the chromosome figured in 18, had condensed 

 into a bivalent without passing through the ring stage. The 

 split then in 18 is the line of the first maturation division. 

 Whether this division is reductional, as believed by Zweiger 

 and Stevens, I cannot say, as I do not know how the chromosomes 



