724 THE AMERICAN NATURALIST [Vol. LI 



kerne, ' ' the origin and fate of which agree with this defini- 

 tion, have been described by Awerinzew in Ceratomyxa 

 drepanopsettce, and in Myxidium sp., by Davis in Sphcero- 

 spora caudata, and by Mavor in Ceratomyxa acadiensis. 



In the disporous form, Sphcerospora dimorpha, two 

 spores are found in the whole animal and the sporogenous 

 body finally contains twelve cells— half of this number 

 forms one spore (Fig. 2). Tliese twelve cells are all 



K K 



°A2 °B2 



0«, Kl ©BII 0b,2 



°m %Zl °B2I °B22 



division products of the one nucleus, the sister nucleus 

 of which is the somatic ' ' Kestkern. ' ' The cells which form 

 the spore membrane of each spore, lying independently 

 in the vegetative body, arise by a very late division. Chro- 

 matic lumps which could be considered as reduction 

 nuclei" are lacking. It is easy to imagine why they are 

 absent. Sphcerospora dimorpha lives in the urinary blad- 

 der and has therefore a metabolism which may not afford 

 opportunity for an abundant glycogen formation. Also, 

 as mentioned before, no reduction of the chromosomes 

 takes place. These facts could be easily ascertained in 

 consequence of the large size of the cells and chromo- 

 somes. Awerinzew 's description of spore formation in 

 Ceratomyxa drepanopsettcc and Mavor's of Ceratomyxa 

 acadiensis have many features in common, but Awerin- 



