ASSORTIVE MATING IN CHROMODORIS ZEBRA 



267 



TABLE 5 



Correlation table for total lengths of 119 pairs of C. zebra obtained in laboratory 

 matings (mass experiments); r = 0.721 =«= 0.02S (cf. Fig. 15) 



the restricted number of matings available for study. Several 

 other influences may also be concerned. In the aquaria the 

 nudibranchs creep over a smooth substratum, and there is less 

 opportunity than in nature for discrepancy in the sizes of two 

 specimens to be discounted by the unevenness of the bottom 

 upon which they might be resting. From this point of view the 

 irregular substratum presented by masses of algae, rocks, and 

 sand would be regarded as favoring the apposition of the genital 

 papillae in the case of two animals differing somewhat as to 

 size. The efficiency of this influence cannot be very great, 

 however; its exact value I am unable to estimate. It is, in addi- 

 tion, entirely possible that some 'pairs' collected in the field 

 were in reality misjudged, in which event the index of regression 

 obtained from the mass experiments w^ould perhaps more nearly 

 represent the true state of affairs. 



The significant point, however, lies in the fact that the lab- 

 oratory matings confirm the qualitative correctness of the con- 

 clusion that there is practiced by Chromodoris zebra a rather 

 intensive degree of homogamy with respect to size (Crozier, 



