(13) 



The "mouth size index" and "mouth form ratio" wor-e computed 

 in the same way. All measurements were made in microns, 

 giving the actual dimensions of the shell. 



The coefficients of correlation given in this paper 

 were computed by the improved methods devised by Dr. Jen- 

 nings (see especially Jennings 1916, p. 416). So many of 

 these constants are given that it seem.s inadvisable to 

 attempt to publish even all of the correlation tables, 

 much less the extensive pedigrees on which they are based, 

 A few of the more important tables are included in the 

 appendix. 



A word as to terminology. In this paper, following 

 the usage of Shull (1912) and Johannsen (1913), the term 

 "pure line" will be considered as restricted to homozygous 

 organisms reproducing by self-fertilization. The various 

 strains of Centropyxis considered in this paper are property 

 to be spoken of as "clones", that is, families arising from 

 a single ancestor by asexual reproduction. The more general 

 terms "strains", "lines" and "races" are considered as 

 synonymous and as having no specific meaning. 



Inheritance within a population. 



Existence of diverse clones. The first requi- 

 site, in any study of inheritance within the asexual pro- 

 geny of a single individual, is to be sure that the diverse 

 clones, whose existence we assume in our population, really 

 exist there. Next one must aemonstrate that there exist 

 between aifferent clones hereditary diversities in the char- 

 acters which are to be studied. Only too often (in the re- 



