LIFE-CYCLE OF " CYSTOBIA " lEREGULAllIS (mINCH.). 33 



never loses its spherical contour, and the material to be 

 expelled is eitlier diffused out at the point where the vacuole 

 is nearest the surface, or else squeezed out, as it were, through 

 a minute rupture in the thin wall. 



Significance of the process. — Opinions differ as to the 

 meaning of the process. Some authors, e.g. Cuenot, attri- 

 bute to it an excretory function, holding that the vacuole 

 contains waste material (" un produit de dechet ") ; others, 

 including Siedlecki, maintain that the karyosome, which they 

 consider to be a stoiehouse of reserve chromatin, is giving 

 back by this means some of its chromatin to the nucleus in 

 readiness for division. Bearing in mind the essential difference 

 between true nucleoli or plasmosomes on the one hand, and 

 karyosomes, where chromatin is intimately bound up with the 

 ground-substance, on the other hand, it seems to me that 

 the latter view has much in its favour. 



I do not mean to imply, of course, that there is never 

 anything in the nature of elimination from the karyosome. 

 Speaking generally, it may be said that, where some of 

 the contents of the karyosome are passed out into the 

 cytoplasm and there become altered, and either expelled 

 or re-absorbed (probably in certain cases being of use to 

 the formative cytoplasm), we have to deal with such a 

 removal of unrequired chromatic material. Instances of 

 this process are seen in Monocystis and Diplocystis, 

 described and figured by Cuenot (loc. cit.), in Lankes- 

 teria ascidiee, according to Siedlecki (loc. cit.), and again, 

 in the case of many eggs, where the expelled grains or 

 spherules can be traced right to the periphery of the cyto- 

 plasm. 



On the other hand, where a portion or all of the karyoso- 

 matic material becomes ultimately incorporated with the rest 

 of the nuclear material, whether by direct dissolution or by 

 fragmentation, it is much more probable that we have to do 

 with a reinforcement of the chromatin of the nucleoplasm. 

 This is almost certainly the case when the dissolution is 

 followed by an increase in the general chromaticity of the 



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