370 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



and if so, when and how this pairing takes place. If, on the other hand 

 there is no such synapsis, how are we to explain the appearance of the 

 chromosomes in the equatorial plate of the first maturation division in 

 only half the somatic number? It is certain, I think, that synapsis of 

 adjacent pairs of chromosomes does not occur in the telophase of the last 

 spermatogonial mitosis. Although Downing (: 05) describes such an event 

 in Hydra, yet his figures, as well as the later history of the spermatocyte 

 nucleus, which, in that form, then passes into a diffuse "resting" con- 

 dition, show, I believe, that his interpretation of the appearances is erro- 

 neous. It is true that in Gonionemus the chromosomes as they approach 

 the poles during the anaphase of the last spermatogonial division are at 

 one period very closely crowded (Plate 3, Figs. 35, 36), but there is no 

 evidence of pairing. This fact is of course in marked contrast to the 

 important discovery of the very early occurrence of synapsis in chilopods 

 (Blackman, :05), Hemiptera (Sutton, : 02), Orthoptera (Baumgartner, 

 :04) and some Amphibia (Montgomery, :03, McGregor, '99), and more 

 nearly agrees with the earlier results of Buckert ('92) on selachians, 

 Born ('94) and Fick ('93), and more recently Meves ('96), on Amphibia, 

 and especially those of Calkins ('95) on Lumbricus. In all these cases 

 where early synapsis has been conclusively demonstrated the chromo- 

 somes, although they may become more or less granular and irregular in 

 outline, retain their individuality from one division until the next (Sut- 

 ton, : 04, Baumgartner, : 04, Blackman, : 05). In Gonionemus, on the 

 contrary, it is quite certain that during the resting stage of the sperma- 

 tocytes the chromosomes, instead of persisting as such, disintegrate into 

 their component granules, part of which mass together to form the nu- 

 cleolus, and although this nucleolus is a chromatin structure, it is not 

 a " karyosphere " in the sense in which Blackman (:05) uses the term, 

 for individual chromosomes do not enter into its make up, nor do they 

 emerge from it during its disintegration. In the prophase of the first 

 maturation division the chromatin forms a distinct chromatin net, in 

 which, on account of the smooth and homogeneous character of the 

 strands, we must suppose that the chromatin granules are very intimately 

 united ; much more so than is the case in either species of Hydra (Guen- 

 ther, : 04, Downing, :05). This net, or rather its chromatin component 

 segments into structures which we may call chromomeres, which are 

 only half as numerous as those of the spermatogonia, but each of which 

 probably contains twice as much chromatic substance as does each of the 

 latter. These chromomeres then unite two and two, and by their fusion 

 form the definitive chromosomes, in half the somatic number, in this case 



