142 SYDNEY J. HICKSON. 



very forcibly that the ovum of Gorgonia does not segment at 

 firsts and that the oosperm nucleus fragments as it does in 

 Alcyonium. 



Arthropoda. — In the development of Peripatus capen- 

 sis, Sedgwick (51) has described the division of the ovum 

 into two blastomeres, and the large and easily seen karyo- 

 kinetic figures which mark the first division of the oosperm 

 nucleus. The fertilised ovum of Peripatus novse-zealandise, 

 however, does not segment, and Miss Sheldon (53) was unable 

 to find any karyokinetic ^gures in the divisions of its 

 nucleus. 



It is a very striking fact in support of my views that in 

 two species of the same genus we should find such a well- 

 marked difference in this respect, the ovum that does seg- 

 ment showing clear and unmistakable nuclear mitosis, and 

 the ovum that does not segment showing no signs of karyo- 

 kinesis. 



But this is not the only example of the relation between the 

 segmentation and the division of the nucleus. 



In a recent paper on the " Embryology of the Macroura " 

 Herrick (6) states that it is a rule with the decapod 

 Crustacea that the nuclei of the segmenting eggs divide with 

 karyokinesis. There is an exception to this rule, however, 

 in the case of Alpheus minus. '^ The fertile e^g of A. 

 minus is pervaded with a remarkably fine reticulum which 

 encloses spherules of minute and uniform size. The nucleus is 

 central or nearly so, and consists of an ill-defined mass of 

 protoplasm, in which a fine chromatin network is suspended. 

 In the next phase the nucleus is elongated and about to 

 divide. Division appears to be direct and irregular. At a 

 somewhat later stage the phenomena of the most interest 

 occur. Each product of the first nucleus has developed a 

 swarm of nuclear bodies which seem to arise by fragmentation. 

 These bodies take the form of spherical nuclei in clear masses 

 of protoplasm. ... In the last stage obtained the whole 

 egg is filled with several hundred very large elements, which 

 are descended more or less directly from some of the nuclear 



