BIGELOW: NUCLEAR CYCLE OF GONIONE.MUS MURBACIIII. 351 



ical constitution of the nuclear structures. The chief nucleolus con- 

 tinues to select the basic dye, and, so far as its finer structure is concerned, 

 shows no differentiation, all its parts, ground substance, vacuoles, fibres, 

 and granules, staining green. The accessory nucleoli, on the other hand, 

 from the time of their earliest appearance to the most advanced stage 

 examined, invariably stain strongly with the acid dye, and thus show a 

 close relationship to the chromatin structures. These two classes of 

 nucleoli are, then, very different chemically, as well as morphologically. 

 All the evidence afforded by the history of the chromatin of the oocyte 

 nucleus goes to show that this substance makes no contribution to the 

 growth of the chief nucleolus, yet the latter body exhibits throughout 

 its entire history the reaction typical of chromatin in active mitosis. The 

 accessory nucleoli, on the other hand, arise in close connection with, and 

 probably as a result of, the metabolic activity of the nuclear reticulum, 

 and their reaction is the same as that of the chromatin structures in the 

 "resting" condition. The theoretic bearings of the occurrence of two 

 distinct types of nucleoli can be discussed better in the general part of 

 this paper, but I may here call attention to one conclusion of general and 

 fundamental importance which is suggested by the staining reactions 

 just described. This is, that in the growth stage, as in all the phases of 

 progressive nuclear activity which I have studied in Gonionemus, mere 

 segregation and condensation of the chromatin microsomes produces no 

 change in their chemical reaction. The reversal of this reaction from 

 the basic to the acid, which is characteristic of them when in active 

 mitosis, is always simultaneous with a striking alteration in the general 

 constitution of the nucleus. In every other prophase of mitosis this 

 alteration consists of a dissolution of the karyoplasm, but Avhether we 

 must seek the same determining factor in the later stages in the pro- 

 phase of the first polar division can be answered only by further 

 researches. 



To examine further the nature of the nuclear structures, I made a 

 series of experiments with chromatin solvents, and with a peptonic 

 digestion fluid ; since, however, I had at hand only fixed material, the 

 results can hardly be expected to be conclusive. Treatment with fum- 

 ing hydrochloric acid, even when prolonged until all chromosomes in 

 mitosis are destroyed, leaves the chief nucleolus entirely unaltered, 

 either in general structure or in staining capacity. The accessory nucle- 

 oli, on the other hand, as well as most portions of the chromatin strands 

 of the oocyte, are usually — not invariably — dissolved. This, of course, 

 is further evidence of the close relations of the accessory nucleoli to the 

 chromatin. 



