LIFE-CYCLE OF " CYSTOBIA " IRHEGULAHIS (mINCh). 45 



some^ when cliff ere iitiated^ causes the appearance, in the 

 cytoplasm of the immediate neighbourhood, of the astral 

 fibres wliicli become united with it to form the complete 

 karyokinetic apparatus.^ 



Indirect nuclear division. — In fig. 51 are drawn many 

 nuclei of botli kinds, taken from a section similar to that seen 

 in fig. 42; the differences between them are now considerable. 

 A typical sexual nucleus in the resting condition is seen at a; 

 at h is another, probably resulting from a recent division, 

 since it has only one attraction-sphere. Dividing stages are, 

 here again, very rare, this being due, undoubtedly, to the 

 relatively slow rate at which the life- history normally pro- 

 gresses in Cystobia. 'i'he commencement of division is 

 shown in c, where the chromatin has left the periphery and 

 occupies a central position, taking the form of grains or little 

 masses; some of these perhaps become dissolved in the 

 nuclear sap, for at d there are only two or three visible. The 

 next stage is seen at c, where the chromatin is stretched out 

 in a thick line or band of grains between the centrosomes, 

 preparatory to breaking up and becoming divided between 

 the two daughter-nuclei. One of the two halves resulting 

 from division is seen at/^ The chromatin is in the form of 

 three or four deeply -staining grains in close association with 

 the division-centre. The nuclear membrane next reappears, 

 the chromatin becomes more spread out, and as the nuclear 

 sap increases in amount, the usual vesicular appearance is 

 regained (/-). The daughter-nucleus is now completely re- 

 constituted. 



Mitosis itself is therefore of a comparatively simple nature 

 in C irregularis, but whether this condition is primitive 

 or secondary I am unable to say. The process most resembles 

 that described by Cuenot as occurring in the nuclei of Diplo- 

 cystis. I have seen no signs of a well-developed nuclear 

 spindle, on which are arranged beautiful V-shaped chromo- 



' Conipaie Hertwig's suggestive ideas (13) respecting the constitution and 

 mutual relationships of the different constituents of living protoplasm. 



