(7) 



a single clone. 



In my ov/n work on Centropyxis, both of these methods 

 tiave been employed, and the evidence drawn frcm coefficients 

 of correlation was used as a guide in the subsequent selec- • 

 tion experiments. 



In closing this brief introduction to the problem, I 

 desire to express my deep indebtedness to Dr. II, S. Jennings, 

 who suggested this problem to me, and who has greatly assis- 

 ted both the experimental work and the preparation of this 

 paper by his kindly advice and criticism. 



Material - Centropyxis aculeata. 



Descriptive. The lobose rhizopod, Centropyxis 

 aculeata Stein, is an excellent subject for genetic investi- 

 gation. It is closely related to Difflugia, the subject of 

 Jenning's recent (3.916) paper and, like Difflugia, its pro- 

 toplasm is surrounded by a spine-bearing shell which fulfils 

 all the requirements for genetic study. That is, it presents 

 definitely meas-oreable structural characters which are her- 

 itable, yet very variable, and which are entirely unaffected 

 by growth or environmental influences during the life of the 

 individual. The shape of the shell is even more favorable 

 for study than that of Difflugia. The individuals used in 

 this study correspond closely to the description of variety 

 discoides Penard (1902). In this form the chitinous shell, 

 studded with sand grains and diatom tests, is decidedly flat- 

 tened (see Figure 2), 'i'f.e upper surface is convex and the 

 lower slightly concave. Seen from above, as in Figure 1, the 

 outline of the shell is nearly circular, and the thin "an- 

 terior" edge, with its smooth outline, is clearly distin- 



