No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 367 



media : immature ova of Sphaer-echimis, placed in sea water to 

 which 1.5 gr, NaCl had been added, show artefacts in the 

 nucleolus : " Each [body] consists of an outer darker shell, 

 which is filled with a clear fluid, and the center of each sphere 

 is occupied by a small black granule " ; several of these struc- 

 tures are usually found on each section through the nucleolus. 

 (For previous descriptions of somewhat similar productions, cf. 

 Ransom ('67), Leydig ('88), and O. Schultze ('87). The upper 

 of the two figures numbered "24" in Morgan's plate should 

 be " 23," since it refers to the nucleolus.) 



Rohde ('96), ganglion cells of Doris and P/eiirobraJic/uis : the 

 nucleoli wander out of the nucleus and finally into the neuroglia, 

 and there acquiring an envelope (derived from the neuroglia) 

 form new cells. [Judging from his figures, however, these 

 supposed nucleoli would seem to be myelin drops.] 



Wagner ('96a), spermatogenesis of Arachnids: " Bei der 

 ersten Spermatocytentheilung theilt sich der Nucleolus ent- 

 weder in der Ebene der Aequatorialplatte mit den Chromo- 

 somen zusammen, oder ausserhalb derselben neben einem der 

 Spindelpole. Im letzteren Falle tritt er nach dem Ver- 

 schwinden der Kernhiille . . . aus dem Kerne heraus." 



Wheeler ('96) gives no description of the nucleoli in the text, 

 but he figures several stages of the development in eggs of 

 Myzostoma (¥\^?>.(^, \o-\i), M. cirriferum ; Figs. 23, 52-54, 56, 

 M. glabrum). In M. cirriferuni (Figs. 12-15) is figured, in 

 addition to the single large nucleolus, also one smaller nucleolus. 



E. B. Wilson ('96) states of the true nucleoli or plasmo- 

 somes : " There is strong evidence that the true nucleoli are 

 relatively passive bodies that represent accumulations of reserve- 

 substance or by-products, and play no direct part in the nuclear 

 activity." In germinal vesicles he assumes that the " principal 

 nucleolus " is chemically different from the nucleoli of somatic 

 cells ; but that the "accessory nucleoli" of the former corre- 

 spond to the nucleoli of the latter. He concludes that " we can 

 hardly doubt the conclusion of Hacker, that the nucleoli of the 

 germ-cells are accumulations of by-products of the nuclear action, 

 derived from the chromatin either by direct transformation of 

 its substance, or as chemical cleavage-products or secretions." 



