NUCLEAR BIVISION OF NOCTILüCA. 247 



In spite of the minor points of differences already given, 

 this remarkable resemblance of the archoplasm of Nociiluca to 

 the centrosphere of Meia.-oa, on the one hand, and to the pole- 

 plate of Protozoa, on the other, makes it in the highest degree 

 interesting as regards the origin of the centrosphere from the 

 pole-plate of Protozoa, and I can not help wondering why so 

 eminent a zoologist as II. Hertwig finds it difficult to place 

 the facts presented by Noctiluca within the domain of his hy- 

 pothesis, that the centrosomes are "selbständig gewordene, ge- 

 formte achromatische Kernsubstanz " ('95. p. 53). In order 

 to bring them into conformity with this idea, it would only be 

 necessary to consider Noctiluca as an animal in w^hich the achro- 

 matic substance of tbe nucleus, which forms the pole-plate in 

 other Protozoa and there remains within the nucleus, has come 

 to be permanently situated within the cytoplasm. At the same 

 time it must be admitted that then a slight alteration has to be 

 made in liis hypothesis to the extent that the entire pole-plate 

 of Protozoa corresponds not to the centrosome, but to Stras- 

 burger's astrosphere ('93), i. e., to the centrosphere together 

 with a centrosome. A similar alteration must also be extended 

 to Heidenhain's conception ('94, (/) of the nature of the achro- 

 matic spindle in Protozoa. This alteration is, however, only of 

 secondary importance ; the fundamental idea of R. Hertwig 

 ('92, a) as regards the position of the kinetic centres in Protozoa 

 and in Metazoa remains unshaken. 



B, Relation of the Archoplasm to the Tentacle. 



In spore-forming individuals, the flagellum is developed from 

 the archoplasmic s])indle-fibres, just as the tail of a spermatozoon 



