(27) 



an average spine number of 1.867. This still gives a dif- 

 ference between the average spine numbers of the high and 

 low groups of .88 ± .07 



The very favorable character of the race employed in 

 experiment 4, that is, the close correspondence between 

 its external appearance and genetic constitution, is shown 

 by the high correlation between parent and progeny. The 

 coefficient Of correlation between parents and progeny, for 

 spine number, is .376 t .017 for the 1277 individuals of 

 this race. This is the highest coefficient of correlation 

 within a clone that has been obtained in the course of my 

 experiments. If the mutation Idl and its offspring are 

 omitted, the coefficient becomes ,282 ± .018. 

 Conclusions . 



Results of the present investigation. The present 

 study of inheritance in Centropyxis may be divided into 

 two parts, the first concerned with a statistical analysis 

 of inheritance within the population and within single 

 clones, the second with an attempt to test the inheritance 

 of variations in a single definite character within the 

 clone, by the method of selection. 



The results of the biometrical study of inheritance 

 in Centropyxis may be summarized as follows. 

 1. There exist in the species , Centropyxis aculeata, many 

 diverse strains or clones which, under identical environ- 

 mental conditions, differ from each other decidedly in 

 spine number, shell size, mouth size and fission rate, but 

 differ only slightly in shell form and mouth form. 



