7 1 2 CALKIxXS. [Vol. XV. 



luca miliaris, where the nucleus and the mitotic figures are 

 quite as complex as in the Metazoa. Ishikawa ('94) had already 

 shown the similarity between Noctiluca and the Metazoa in 

 this respect, although his account of mitosis in the former was 

 incomplete. Noctiluca holds so important a place in the series, 

 especially in relation to the process of mitosis, that its nuclear 

 division should be fully and accurately known, and it has been 

 my aim during the last two years to clear up, if possible, the 

 points still left obscure. 



The wide distribution of Noctiluca and the large size of its 

 nuclear elements have made it a favorite subject for research, 

 although it has seldom been studied from a cytological stand- 

 point. Huxley's description ('55) was purely morphological, as 

 were those of De Ouatrefages ('50), Krohn ('52), and Busch 

 ('55). Brightwell ('57), describing the external phenomena of 

 cell division, undoubtedly saw the sphere,^ but called it a 

 secondary nucleus. Cienkowsky ('71 and '73) described the 

 external features of spore-formation, but without reference to 

 the nucleus or the accompanying structures. Robin ('78) in 

 his description of the spore-formation seems to have mistaken 

 the sphere for a nucleus, and his accurate illustrations tell more 

 about the nuclear processes of division than the te.xt. 



It was Ishikawa ('94) who first gave accurate details of 

 mitosis in Noctiluca. His work can best be reviewed by pre- 

 senting his own summary (pp. 324-326) as follows : 



1. The division of the animal is preceded by the loss of the peristome, 

 teeth, and the tentacle, the last of which is not thrown off, as Robin is 

 inclined to think, but is redrawn into the body of the animal. The mouth 

 and the " Staborgan " are, however, always present (Robin). 



2. The spore-forming individuals differ from the dividing ones in not 

 possessing the mouth and Staborgan in addition to the organs above men- 

 tioned, and by the excessively empty appearance of the cell interior 

 (Cienkowsky). 



3. The division of the nucleus is always preceded by a concentration of 

 a part of the cytoplasm in the form of a spherical or oval granular body, 



' I use the term " sphere " to designate the large, clearly outlined cytoplasmic 

 mass which is probably to be identified as an attraction spfiere. During the pro- 

 phase of mitosis it divides and forms anamphiasterwith connecting central-spindle 

 fibers, and in the anaphase a centrosome is found within it. 



