498 Wisconsm Academy of Sciences^ Arts^ and Letters. 



blue stained diromatin network that can always be clearlv seen 

 in good preparations. The nuclear membrane is quite sharply 

 differentiated and sometimes stands out as a deeply stained 

 thick boundary. 



While the above general statement is true for all of the 

 nuclei there is a remarkable individual variation both in ap- 

 pearance of contents and in form and size. In a typical rest- 

 ing stage the nuclei are generally quite small spherical bodies 

 with the chromatin arran^red in a verv fine sli£:htlv stained, but 

 verv clearlv visible network. At various places in the net the 

 chromatin appears to be more or less collected into limips. 

 Very frequently in cells showing great vegetative activity, as 

 for example, in the grow^tli of the young nets or in cases in 

 which starch is being rapidly formed the nuclei become quite 

 large and vesicular in appearance (See Figs. 41 and 42. Cf. 

 also Fig. 1 in my paper on starch formation in Ilydrodictyon). 

 In these cases the chromatin frequently appears as very fine 

 lines radiating from the prominent central nucleole to the periph- 

 ery. Unless the preparations are well stained the chromatin 

 in such cases might be easily overlooked, but in no stages of cell 

 life have I been unable to demonstrate a clear differentiation 

 of the nuclear contents into chromatin and nucleole. 



Spherical nuclei with the contents arranged as above de- 

 scribed are always found in cells showing no signs of reproduc- 

 tive activity. In all cases, however, in which cleavage is tak- 

 ing place the chromatin is collected into denser roughly elon- 

 gated masses taking a deeper stain and connected by fine 

 threads as of linin (Figs. 24-32). 



The nucleole becomes much less sharply defined in these than 

 in the resting stages just described and in some cases is so sur- 

 rounded by the chromatin as to be almost indistinguishable. 

 The whole structure of the nucleus is in fact identical in ap- 

 pearance with the early prophases or late anaphases of division. 



The nuclei vary in shape from the S2:)herical forms just 

 described to those with verv irreinilar outlines, some of which 

 are quite sharply angular, while others have blunt rounded ex- 

 tensions resem.bling the pseudopods of an amoeba. In many 

 cases, especially in cells in process of cleavage, the nuclei are 



