MITOSIS AND AMITOSIS. 409 



found in the incomplete separation of daughter nuclei or in 

 chromatic connections between them. Thus Gurwitsch (1905) 

 has figured and described the division of a blastomere of a 

 centrifuged Triton egg in which two nuclei, connected by a 

 chromatic thread, are dividing by mitosis. The chromatic 

 connection is taken as proof positive that the nuclei had divided 

 by amitosis and Godlewski (1909) in a general review of this 

 subject, after dismissing as doubtful many other cases in which 

 amitosis had been reported as occurring in normal development, 

 falls back upon this case described by Gurwitsch as one of the 

 strongest evidences in favor of the view that amitosis may occur 

 in normally differentiating cells. 



But chromatic connections between nuclei are not to be taken 

 as positive evidence that those nuclei have divided by amitosis, 

 for these connections may be the result of incomplete or atypical 

 mitoses. Anything which retards or prevents the separation of 

 daughter chromosomes may lead to the scattering of chromo- 

 somes along the spindle or to their elongation into threads and 

 consequently to the formation of chromatic connections between 

 daughter nuclei. Hacker found such connections in etherized 

 eggs of Cyclops and such connections are present also in Crepidula 

 eggs subjected to high temperatures (Figs. 6, 8), to hypertonic 

 sea-water (Fig. 29), and to hypotonic sea-water (Figs. 49-60). 

 It is especially in the last named experiments that chromatic 

 connections between daughter nuclei are most frequently seen 

 and they merit a detailed description. 



The eggs shown in Figs. 49-54 were placed for one hour in 

 sea-water diluted with two volumes of fresh water and were 

 then returned to normal sea-water for four hours before being 

 fixed; those shown in Figs. 55-60 were placed for two hours in 

 sea-water diluted with one volume of fresh water and were then 

 left in normal sea-water for fourteen hours. In all of these 

 cases the centrosomes divided normally and approximately 

 normal spindles were formed but the separation of chromosomes 

 and the formation of daughter nuclei were atypical. In Figs. 

 9, 29, 49 and 50 the scattering of chromosomes is shown in some 

 of the spindles but more notable than this is the stretching of 

 chromosomes into long threads some of which run from one 



