Internal Characteristics and Size 1 1 1 



This similarity of mates is termed "assortative mat- 

 ing". The coefficients of correlation for the lengths 

 of the two members of a pair were between +0.43 and 

 +0.79 in five cultures studied by Pearl. Similar co- 

 efficients, averaging +0.38 were found by Jennings 

 ('11) in mixed populations. 



But even within a clone there was considerable as- 

 sortation, giving a coefficient of +0.25 (Jennings, '11). 



Assortation of body lengths between mates was 

 found not to occur in Chilodon by Enriques ('08). 



In the parasitic ciliate Anoplophrya Collin ('09) ob- 

 served it; but here the possibility remained that the 

 extremely different-sized individuals, which did not 

 mate, belonged to different clones. 



Watters ('12) demonstrated in the ciliate Ble- 

 pharisma that conjugants are smaller and that they 

 mate assortatively. Calculations from the frequency 

 curves which were published show that the variability 

 in length for non-conjugants was 16.9, for all conju- 

 gants was 10.3, and for actual pairs was 7.2. This 

 genus is entirely similar in assortation, therefore, to 

 Paramecium caudatum. 



Assortative mating with respect to body length was 

 found and measured in several species of parasitic in- 

 fusoria by Dogiel ('25) and Poljansky ('26). Al- 

 though the hereditary origins of the individuals were 

 not controlled, remarkable uniformity of sizes oc- 

 curred throughout the general populations studied. 



Mating, then, presents a physiological process which 

 requires a high degree of similarity between the mates 

 for its successful accomplishment. Through the size 

 prerequisite, mating tends to bring together not only 

 similar ages, but also like hereditary constitutions. 

 Size is a visible means of discouraging the mixing of 

 races. 



