BIGELOW: NUCLEAR CYCLE OF GONIONEMUS MURBACIIII. 291 



('83) seems to have been the first to distinguish between chromatin and 

 achromatin in this group ; and to reach the conclusion that the nucleus 

 in coelenterates is of the ordinary metazoan type : a conclusion supported 

 by Schneider ('92) and Bidder ('95); and, for sponges, by Fiedler ('88). 

 Sharply opposed, however, to this view, is Chatin ('90), who believes 

 that the nuclei in sponges exhibit decided protozoan affinities. 



Hardly more extensive than the literature treating of the resting so- 

 matic nucleus in coelenterates is that dealing with somatic mitosis. The 

 earliest study, from a modern standpoint, of this form of nuclear division, 

 is that of Pfitzner ('83), who, evidently stimulated by Flemming's ('79, 

 '80) recent discoveries, examined the process in Hydra. Considering the 

 small size of the cells, and the methods employed, his work is excellent, 

 and deserves more attention than it has received. Moreover, it remained, 

 until very recently, the only detailed account of the indirect division of 

 the somatic cells of a coelenterate. Pfitzner, as already mentioned, dis- 

 tinguishes in the nucleus two substances, chromatin and achromatin; he 

 traces the fate of the former during division, finding that in all import- 

 ant features it conforms to Flemming's ('82) scheme. Five years later 

 Fiedler ('88) described the mitotic figures in sponges; his account is, so 

 far as I have been able to learn, the only detailed one of the process in 

 the adult tissues of this group which has yet appeared. His most im- 

 portant advance over Pfitzner's ('83) earlier work is his ('88, Figs. 30, 

 31) discovery of the longitudinal splitting of the chromatin rods, and his 

 detection of the centrosome. 



The only recent account of somatic mitosis in the adult tissues of a 

 coelenterate with which I am acquainted, is a brief description by Down- 

 ing (: 05) of the process in the interstitial cells of Hydra. 



2. Spermatogenesis. 



The beginning of modern knowledge of spermatogenesis in coelenterates 

 may well be dated from the researches of Eimer ('72), who showed that 

 the spermatozoa were entire metamorphosed cells ; not parts of cells or 

 cell derivatives as F. E. Schultze ('71) and Kleinenberg ('72) had sup- 

 posed. This discovery, moreover, was substantiated by Varenne ('82), 

 who further observed that they arose through repeated nuclear divisions 

 on the part of the sperm mother cells, a result upheld by Polajaelf ('83), 

 Merykowsky ('82), and von Lendenfeld ('83). Thallwitz ('85), who 

 made the first study of the nuclear changes in the spermatogenesis of 

 coelenterates, concludes that, in hydroids at least, the cell divisions pre- 



