NOTES ON SOME PROBLEMS OF ADAPTATION: 6. RE- 

 LATION OF LIGHT TO THE PIGMENTATION 

 OF ASCIDIANS. 1 



W. J. CROZIER, 

 ZOOLOGICAL LABORATORY, RUTGERS COLLEGE. 



I. Experiments concerned with the re-formation of the test 

 of the blue-black Ascidia atra, subsequent to its injury or partial 

 removal, have demonstrated (Hecht, 'i8a, p. 236) that "the 

 newly formed test material is pigmented in the usual way," 

 even in the case of animals operated upon at night and main- 

 tained during regeneration in complete darkness. Since, "more- 

 over, a new, pigmented test will form on the right face of the 

 animal under the intact, opaque, old one, when the latter has 

 been accidentally separated from the ectodermal surface which 

 secretes it," Hecht concluded that the characteristic pigmenta- 

 tion is not due to the presence of light in the sense, at least, 

 that it cannot result from "a photic stimulus only." This con- 

 clusion is of interest, since it at first sight conflicts with some facts 

 afforded by related species, and also with facts which may be 

 made out from the distribution of A. atra itself in nature. 

 Hecht's experimental result I can fully confirm, but inasmuch as 

 pale, relatively unpigmented individuals are to be encountered 

 in dark situations, the relation of the illumination to pigmenta- 

 tion seemed far from clear. 



It might be assumed that if, in the normal course of develop- 

 ment, pigmentation were simply a qualitative result of metabolic 

 events, the quantitative course of transformations leading to 

 pigment deposition in the test might be determined, once for all, 

 by illumination early in the ascidian's life; if this were correct, 

 experiments upon adult animals might be quite incompetent to 

 decide whether or not light has anything to do with pigmenta- 

 tion and effects substantially of this category are not unknown 

 (Goldfarb, '10). 



1 Contributions from the Bermuda Biological Station for Research, No. 132. 



1 06 



