NOTES ON SOME PROBLEMS OF ADAPTATION. 115 



individuals, is no more acceptable as food than that of the 

 blackish specimens. The different degrees of pigmentation are 

 determined, so far as one may judge, by quantitative differences 

 in the capacity for producing the single type of pigmentary 

 substance concerned. So far as available evidence permits one 

 to say, it is as reasonable to hold that the immunity of Stichopus, 

 however achieved, permits its pigment-forming power to de- 

 velop unhampered by selective restraint, as to believe that a 

 kind of "warning" coloration is being elaborated selectively. 

 In this respect the diverse types of coloration found in the 

 efficiently protected snail Onchidium (Crozier and Arey, '19) 

 provide an interesting parallel. And in Chromodoris (Crozier, 

 '19), as I shall subsequently describe at length, the evidence is 

 much more decisively of the same import. Questions of this 

 sort, particularly as concerned with the matter of so-called 

 "warning" coloration, have been, in my belief, on the whole 

 so inadequately dealt with that even partially complete observa- 

 tions seem worthy of presentation. 



Summary. -The coloration of Stichopus wcebii is quite vari- 

 able, in some individuals probably of a concealing tendency, in 

 others, the majority, of a sort which makes these animals in 

 nature pronouncedly conspicuous. Perhaps conditioned by the 

 bulk of the animals, possibly by the presence of a repugnant 

 quality of the flesh, such as leads to the rejection by fishes of 

 fragments offered as food, a decided immunity from gross attack 

 is, at all events, achieved. There is no more reason to regard 

 the conspicuous type of pigmentation as a warning agent than 

 there is to consider it the unchecked expression of innate meta- 

 bolic activities. 



CITATIONS. 

 Bartsch, P. 



'17 Pirates of the Deep Stories of the Squid and Octopus. Ann. Kept. 



Smiths. Instn. for 1915-16; Append., pp. 347~375- 

 Chatton, E. 



'09 Une ascidie fixee dans la peau d'Holothuria tubulosa Gm. Bull. Soc. 



Zool. Fr., T. 34, pp. 25-27. 

 Crozier, W. J. 



'15 A Note on the Physiology of the Cuvierian organs of Holothuria captiva 



Ludw. Amer. Jour. Physiol., Vol. 36, pp. 196-202. 

 '16 On the Immunity Coloration of Some Nuclibranchs. Proc. Nat. Acad. 



Sci., Vol. 2, pp. 672-675. 



