30 THE NAUTILUS. 



SEX-CORRELATED COLORATION IN CHITON TUBERCULATUs. 1 " In 

 adult chitons of this species [in Bermuda] there is noticeable 

 what appears at first sight to be a considerable diversity in the 

 degree to which pigment, of a salmon-pink hue, is developed 

 upon the foot and other soft parts exposed in ventral view. 

 Somewhat less than half of the individuals have the foot, 

 ctenidia, and other soft parts exposed in ventral view. Some- 

 what less than half of the individuals have the foot, ctenidia, 

 and other soft parts of a pale buff color; in the remainder, the 

 foot, head, ctenidia and mantle are to various degrees tinged 

 with salmon-pink or startlingly vivid. This difference is most 

 pronounced during late spring, but persists to some extent 

 throughout the year. The pigmentation is not correlated in 

 any way with size; individuals of any length from 3.4 to 9.2 

 cm. may be either pale buff or salmon-pink on the ventral sur- 

 face, nor does the intensity of reddish pigmentation, when 

 present, depend upon size. In dorsal view it is quite tmpos- 

 sible to distinguish the two groups of animals, unless the plates 

 be artificially separated to an extreme degree and not even then 

 with any certainty. 



" The differential coloration proves to be correlated with sex, 

 in the sense that the soft parts of male chitons are never colored 

 pink whereas those of maturing females invariably are, the in- 

 tensity of the pigmentation depending to a large extent upon 

 the state of maturity of the ovary, to a lesser extent, it seems 

 probable, upon the quantity and the kind of the algal food 

 available in differing environments. 



"The color difference between the sexes of chiton is believed 

 to be of special significance, for the following reasons, because 

 the coloration of the soft parts of the female is directly traceable 

 to metabolic activities associated with the growth of the ovary, 

 and because it provides an example of secondary sexual colora- 

 tion which has no conceivable utility, but is, on the contrary, 

 so far as color is concerned, of a thoroughly accidental nature." 

 W. J. CROZIER. 

 DYER ISLAND, BERMUDA. 



1 Extracts from a more extended discussion under this title in The Amer- 

 ican Naturalist, Jan. -Feb., 1920, pp. 84-88. 



