(10) 



the new shell is completely produced by the parent organism 

 before nuclear division begins. It is simply handed onto one 

 of the productB of tlie ensuing fission. Further, the new 

 shell is in no sense molded on the old one. This is particu- 

 larly evident in Centropyxis, since, as figure 3 shows, the 

 axes of old and new shells lie ir: exactly opposite directions 

 The number of spines and the shape of the shell, then, must 

 be determined by precisely the same kind of determiners that 

 underlie all the other hereditary characters of the species. 



Previous breeding work on Centropyxis, The only 

 other investigator who has studied the reproduction of Cen- 

 ti-cpyxis aculeata is f^chaudinn (1903, 1911). In his account 

 of the life history of this species, he includes a few notes 

 on the vegetative reproduction, f/ost of these statements 

 I have been unable to confirm. Ke states, for instance, 

 that the new shell is always larger than the old one. This 

 I find not to be true. The new shell may be either slightly 

 larger or slightly smaller than the old one. In line 30 

 ( to be described later ), with over 750 recorded fissions, 

 the average size index of the parents was 21,969 sq. microns, 

 that of the offspring 21,624 sq. microns. Schaudinn also 

 says that he was never able to get an individual to divide 

 more than once, and concludes that after this single fission 

 the old individual lives on for some time ar.d firally dies. 

 In my cultures, individuals have repeatedly divided as 

 many as ten times, som.e as many as fifteen times. 



I have made no experiments on the sexual reproduction 

 of Centropyxis, and will not discuss the life cycle. It 

 is briefly described in Schaudinn 's paper (1903). I car 



