250 Actinosphaerium Elchornl 



had beguu to eucyst. The threc iudividuals which wcre allowcd to leach the 

 conjugation stage had cysts of the foUowing dimensions : 



(a) 1 cyst=8'31^, 15 cysts = 8'75 /x. 



(6) 2 cysts = 8'7.5, 1 cyst = 8"31. 



(c) 4 cysts =8-31. 



The cysts built by these individuals, then, were all large (cf. Table III.) : from 

 which we may safely judge that thcy were few in ix'lation to tlie organisms' size. 

 And yet we have seen that the organisms possessed many nuclei after beiug fed in 

 the cold : but this seems to have had no effect in detcrmining how many nuclei 

 should be preserved for the process of encystment. This expeiiment shows in 

 a striking manncr that it is the tcmperature at the time of encystment which 

 determines to an overmastering degree the number and in consequence the size of 

 the cysts to be forined. 



3. As the corollary to the above two experiments I may niention that I 

 kilied and stained the non-encysted weediugs from both hot and cold starvation 

 cultures in numerous instances, but was never ablu to find the slightest cvidence 

 that an increase of nuclei had taken place in the cold or a decrease in the warmth, 

 in such a way that by this means tlie differeiit numbers of nuclei retaincd for 

 encystment in the two cases miglit bc accounted for. 



G. In what way does the size of the cyst atfect the nucleus (chromatiu) 

 contained ? 



I must preface the following section, which constitutes the crucial part of the 

 investigation, by drawing a distiuction bctwuen the nucleus as a morphological 

 entity and the chromatin as a physiological cntity characterizing the former. 

 We are not concerned here with a change of size of the nucleus as a morpho- 

 logical structure, a change which could bc brought about by an alteration in the 

 conditions of tension in the cell without any deeper changes in the physiological 

 relations. But we are concerned with a change in the relative proportious of 

 chromatin, the distinctive property of the nucleus, to the cytoplasm ; and the 

 question to be answered is, In the different sizod cysts does the chromatin rcmain 

 of a constant mass so that a different reiation of chromatin and cytoplasm is to be 

 observed in tlic different sized cysts, or has the cell the power of readjusting the 

 reiation betwecn chromatin and cytoplasm ? The reader must turn to Plate II. 

 for an answer. These figures, drawn to scale, represent scctious* through con- 

 jugation cysts built in the warmth, Plate II., in the cold, Plate III., and at room 

 tcmperature, Plate IV. 



• Owing to the opacity of the cysts I was obliged to cut aections of them in all cases. Tlie thickness 

 of the cyst coats makos them vcry diflicult to preservc. I first used Picroacetic acid which distorts the 

 cytoplasm (Figs. o — y), subsequently I used Perenni's fluid which is more satisfactory (Figs. i—i"), the 

 fact that the cytoplasm in Figs. a — y is distorted does uot alTcct the reiation of chromatin to cj'toplasm ; 

 the size of the cyst may be roughly judged by the outline of the cyst coat and the mass of chromatin 

 would not be altered by the prescrving fluid used. Purists in Histology may neglcct Figs. 5 — f, and 

 convince themselves of the maiu truth of the argument by tbe similarly ill-preserved figures. 



