ZOOLOGY: W. J. CROZIER 



521 



ence sufficiently evident. Measurements of these pairs are plotted in 

 figure 2. The correlation between the members of mating pairs is in 

 fact better than in the previous case (fig. 1); reasons for this will be 

 discussed in a subsequent paper. 



A study of the behavior of Chromodoris supports the view that there 

 is exercised an active selection of mating partners. As a rule, two ani- 

 mals greatly differing in size do not successfully copulate. This has 



I I 



I I 



Fig. 1 



Fig. 2 



FTG. 1. ILLUSTRATING THE CORRELATION IN SIZE BETWEEN THE MEMBERS OF 148 PAIRS 

 OF CHROMODORIS ZEBRA COLLECTED IN THE FIELD 



The thin continuous line (1) gives the lengths (as ordinates) for the different classes of 

 individuals in order of decreasing size. The heavy line (2) gives the average lengths of the 

 mates of the individuals of these classes. The unit is 1 cm; m m' is the mean for all. 



FIG. 2. ILLUSTRATING THE CORRELATION IN SIZE BETWEEN THE MEMBERS OF 119 PAIRS 



OBTAINED IN LABORATORY EXPERIMENTS 



The thin continuous line (1) gives the lengths (as ordinates) for the different classes of 

 individuals in order of decreasing size. The heavy line (2) gives the average lengths of 

 the mates of these classes. The unit is 1 cm; in m' is the mean for all. 







been verified by experiments in which the size of some individuals 

 has been artificially reduced through starvation. The physical basis 

 of assortive mating in Chromodoris is probably found in the relative 

 attitudes assumed by the conjugants and in reactions to tactile (and 

 chemical?) stimuli which determine these attitudes. 



Two suggestions may be made regarding the possible significance of 



