i893. NUCLEUS IN UNICELLULAR ORGANISMS. 177 



endeavour to study alone the behaviour of the nucleus, both before 

 and during, as well as after, the various steps in the cyclic changes 

 undergone by this cell. 



A magnification of from 5,000 to 6,000 diameters was found 

 efficient for this, and with the life-history of the cell known, it was 

 less difficult to trace by themselves the nuclear changes. 



In studying these, it is only the changes occurring and observed 

 in the living organism, and during its life, that have proved of any 

 real value. The effect of desiccating and staining these saprophytes 

 was in all senses unsatisfactory ; the details were too minute, or too 

 delicate to admit of this treatment, for whatever method was adopted, 

 the results, as compared with the living form in the same stage, were 

 simply unintelligible and useless. But this could only be really seen 

 by comparison of the results of the same phenomenon in the living 

 organism, and in the dried and stained state. 



Nevertheless, by using a one-and-a-half per cent, of acetic acid, to 

 which varying quantities of methyl-green are added, a decided 

 strengthening of the special nuclear features was effected. Thus the 

 nuclear envelope seen in most stages of its activity is much 

 strengthened, and so were the beaded threads embedded in the nuclear 

 hyaloplasm ; and little, if any, inconvenience could be seen to result 

 in the organisms. 



In the inactive stages of the organism, or when no cyclic changes 

 were manifest, the nucleus was hyaline, or at least exhibited nothing 

 but the faintest traces of a colourless reticulation when very critically 

 examined. This simple state of nuclear hyaloplasm is seen in Fig. 13, 

 representing a portion of the body of the organism and the nucleus, 

 the latter magnified 5,000 diameters. 



By steadily watching a form in this condition, it would in all 

 probability be seen to become more marked in its granulation, and at 

 length what appeared like a delicate thread of beaded structure 

 became more and more visible, occupying at first the circumference 

 and at length the whole plasm of the nucleus, as shown in Fig. 14 ; but 

 when this was complete a distinct line, made more visible by methyl- 

 green, appeared, as shown in the nucleus of that figure. No indica- 

 tion of any division anywhere in the body of the organism had yet 

 appeared. Now, however, it soon becomes manifest that the complex 

 foldings and twistings of the beaded thread in the nucleus condense 

 on either side of it, leaving the dividing line in a hyaline space, as 

 shown in Fig. 15 ; and now for the first time a line appears at a and 

 opens, so that the fission of the body has begun. 



After this the process is rapid, occupying only three or four 

 minutes. The nucleus opens as in Fig. 16, where it is seen apart 

 from the body, corresponding to the stage seen in Fig. 2, D, rapidly 

 passing into the condition seen in Fig. 17, corresponding to the 

 state shown in Fig. 3, E, and where the fine-beaded thread appears 

 to be drawn out, connecting the still dividing nuclei ; but in this 



N 



