BLACK.MAN: THE SPERMATOGENESIS OF SCOLOPEXDRA. 89 



chromatin reticulum in resting stages is exceptional, being found in only 

 a very few of the most highly developed nuclei. In Metazoa these 

 "chromatin nucleoli," while not of such general distribution, arc present 

 in a large number of both somatic and germ cells and in some groups 

 seem to be of nearly universal occurrence. In the Choi-data they are 

 found in a number of groups ; in the Ascidia (Distaplia, Davidoff, '89), 

 in amphibians (Salamandra, Rabl, '85; liana and Triton, Schultze, '87; 

 Ran a and Neeturus, Macallum, '91 ; Axolotl, Fick, '93 ; Diemyctylus, 

 Jordan, '93 ; Salamander, Metzner, '94 ; numerous Batrachia, Carnoy et 

 Lebrun, '97, '98. :00) ; in Aves (Pica, Mertens, '94), and in mammals 

 (Mus, Hermann, '89, Holl, '93, Sobotta, '95). I have myself seen similar 

 appearances in the germ cells of reptiles (Eutaiuia and skink), but have 

 never studied them in detail. A like condition exists in the germ cells 

 of numerous arthropods, according to Carnoy ('85). Karyospheres are 

 certainly present in all the principal genera of Chilopoda (Carnoy, '85 ; 

 Blackmail, :0l). 



Chroinatin-bearing nucleoli are not confined to animal cells, but are 

 found in the cells of many plants as well. Their presence is vouched for 

 in Spirogyra by Meunier (86) and Moll ('93). Meunier says: " Nous ne 

 craignons pas d'affirmer que le nucleole des Spirogyra reproduit fidele- 

 ment, dans ses traits essentiels la structure des noyaux les plus parfaits 

 . . . quoi qu'il en soit, nucleole par position, noyau par nature, on ne pent 

 lui refuser le nom de nucleole noyau, dans le sens attache a ce mot par 

 J. B. Carnoy." In diatoms (Lauterborn, '96) the nucleoli contribute to 

 the formation of the spireme, and in Fritillaria (Heuser, '84 ; Strass- 

 burger, '84) a similar condition exists. 



These pseudo-nucleoli vary considerably in their general characteristics, 

 from small globules of pure chromatin, found in some cells, to the highly 

 complex karyospheres present in Amphibia and Myriapoda. Of these the 

 most complex type is probably represented in the spermatocytes of the 

 Chilopoda, where this structure contains all of the essential elements of 

 a nucleus, — chromatin, karyoplasm, and karyolymph. The same type 

 also occurs in Protozoa (Actinosphaerium) and in plants (Spirogyra). In 

 Amphibia there are a number of "nucleoli," but they still are character- 

 ized by the reticular structure. In the majority of these nuclei the 

 chromatin elements have been shown to be derived from the " nucleo- 

 lus," either entirely or in part. 



It seems strange that the occurrence of phenomena observed by so 

 many cytologists should not be credited or should be received only with 

 scepticism by the majority of their co-workers, but such appears to be 



