556 Mr. J. E. S. Moore and Miss A. L. Embleton. [Dec. 5, 



maiotic (homotype) division. Consequently these two divisions with their 

 respective prophases form a stage in the cell cycle of plants and animals 

 which differs entirely from the divisional sequence before and after it. 



The present communication deals with the prophase of the first maiotic 

 division in Triton, and with the subsequent division up to the appearance of 

 the diaster. As we have worked out the stages in this animal in great 

 detail, we propose to give the results of our observations without discussion 

 in the text, but to indicate by means of footnotes those points in which the 

 fresh observations differ from the existing accounts of the maturation process 

 in general, and of the same phenomena among amphibia in particular. 



It may however be pointed out that the results of this investigation have 

 been entirely to confirm the general interpretation of the maiotic meta- 

 morphosis already published by Professor Farmer and one of ourselves.* 



At the same time it should be noted from the beginning that this view of 

 the maiotic process entails a complete revision of the older conceptions of the 

 nature of the first maiotic (heterotype) division among the higher vertebrata, 

 such as those embodied in the able works of Hemming, Meves, and many 

 others. 



During the early summer (June) in England the testes in Triton are 

 found to present all the phases in the cell cycle, from premaiotic cells 

 dividing in their characteristic manner, to the spermatids that have been 

 produced by the second maiotic (homotype) division (see fig. 1, Plate 20). 



From this figure it will be seen that in the section of the testes which 

 the drawing represents the spermatogenesis is proceeding from the top 

 towards the bottom of the Plate. Immediately below the peritoneal attach- 

 ments groups of cells are seen, some with their nuclei at rest, others dividing ; 

 while in the region marked (c) nuclei are seen as we pass downwards, which 

 are at first indistinguishable from those in (b), but which gradually alter in 

 the appearance until we reach the lower part of (c). 



The division figures encountered in region (&) are all of the ordinary 

 premaiotic type, and the appearance which comes over the resting nuclei in 

 (c) as we pass downwards is the appearance produced by the advent of the 

 synaptic metamorphosis in Triton when seen under a low power. Still lower 

 than the region (c) the two maiotic divisions (heterotype and homotype) are 

 encountered together. 



The above will serve to orientate the original and relative positions of the 

 cells which have been taken as individual illustrations of the successive 

 phases of the synaptic change. But before leaving the small scale figure, it 

 may be noted that upon examination the resting nuclei in region (b ) differ 



* Farmer and Moore, loc. cit. 



