NOTES ON SOME PROBLEMS OF ADAPTATION: 7. RE- 

 GARDING THE PIGMENTATION OF STICHOPUS 



MGEBII. 1 



W. J. CROZIER, 

 ZOOLOGICAL LABORATORY, RUTGERS COLLEGE. 



The large holothurians of the genus Stichopus, which are quite 

 abundant at Bermuda, live for the most part in fairly shallow 

 water and upon grass-free bottoms of sandy mud. The majority 

 of the individuals, but not all, are quite darkly pigmented. 

 They are consequently open to the view of fishes and of other 

 predaceous creatures, their coloration being in the great majority 

 of cases very far from "concealing" in character. I was curious 

 to learn if this lack of concealment was in any way related to size, 

 or to the presence of some repugnatorial property. These 

 holothurians do not possess Cuvierian organs. 2 



About 70 per cent, of the individuals are dorsally of a deep 

 brown or even blackish hue, some 20 per cent, being light brown, 

 with a distinctly yellowish cast, and the remaining 10 per cent, 

 very pale brown with a pinkish shade. About 75 per cent, of 

 the two kinds of lighter-colored specimens show a series of circular 

 dark blotches, located at the bases of the scattered podia. A 

 small proportion are irregularly mottled or blotched with areas 

 of dark pigmentation. The pale spotted individuals are in 

 many instances very difficult to detect, especially if located 

 among algae and corals on an inclined shore; on a bare mud 

 bottom they are more easily seen. The amount of pigment in the 

 integument bears no definite relation to age (size). 



1 Contributions from the Bermuda Biological Station for Research, No. 133. 



2 I have vainly sought for instances in which the well-developed Cuvierian organs 

 of Holothuria captiva (Crozier, '15) might be seen in action (cf. Cuenot, '98). This 

 species sometimes lives, under stones, in association with the large annelid Hermodice 

 caruncidata, which is armed with powerful groups of long, sharp seta?; but I have 

 never seen evidence of disturbance of the holothurian by the annelid. The tubes 

 of the Cuvierian organ when discharged in air and received on filter paper (or on 

 the tongue) are never acid in reaction; apparently their sole utility is in connection 







with their tensile strength and adhesive power. 



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