No. 630] SHORTER ARTICLES AND DISCUSSION 85 



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

 pink; whereas those of maturing females invariably are, the 

 intensity 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 avail- 

 able in differing environments. 



I have been at some pains to verity this conclusion by numer- 

 ous dissections and by microscopic examination of smears from 

 the gonad of 129 individuals. As in most chitons, the nature of 

 the single median gonad is readily distinguishable, when mature 

 or nearly so, owing to the fact that ovary and testis are differ- 

 ently colored. In the case of the young C. tuberculatus, and of 

 the immature gonad in animals of all sizes, testis and ovary are 

 macroscopically undistinguishable, being pigmented in the same 

 degree by a brick-red substance, which will be referred to in 

 what follows. These observations were made for the most part dur- 

 ing the week ending March 30, 1918, at which time motile sperms 

 and well-developed (but not mature) eggs were present. The 

 ripe testis differs in color from the ovary because the amount of 

 red pigment in the stroma of the male gonad does not increase 

 after a very early stage ; so that the testis comes to appear as a 

 milk-white organ with innumerable interlacing threads of dull 

 crimson upon its surface. In the ovary, on the contrary, the 

 amount of this red substance increases enormously. No trace of a 

 gonad was detected in 72 animals less than 3.4 cm. total length, 2 

 the smallest female being 3.4 cm., the smallest male 3.4 cm. also. 

 A group of 67 individuals between 3.4 and 9.2 cm. length, col- 

 lected at random, was examined by first carefully noting the 

 coloration of the tissues (foot, etc.), then investigating the con- 

 dition of the gonad. Among these 67, 27 were males containing 

 active sperm; the foot, ctenidia, and other parts were m every 

 case pale buff in color. The remaining 40 were clearly separable 

 from the others by the presence of pink or orange pigment, and 

 were without exception females. A further group of 64 chitons 

 was first divided into two lots, "pale" and "pink," respectively ; 

 smears and teased preparations of the gonads showed that in 

 only two instances was the expectation based upon the group 

 first studied defeated, and in these instances the animals were 

 small females with very immature ovaries. Summarizing the 



