THE RELATION JJETWEKN EIGHT AND PIGMENT-FORMATION. 557 



types may be combined in a single brood in the proportion of 

 36 per cent, dominant or pigmented forms. 



Tlais result at once suggests that green in the parent is of 

 twofold origin; and the facts of earlier experiments support 

 the suggestion. It has been shown (Gamble and Keeble) 

 that green is both an independent stable colour-form and 

 also a colour assumed by brown specimens on a transfer to 

 green weed. Further experiments are necessary to decide 

 whether the green parents with recessive red colouring are 

 of the former type, and those with more dominant red 

 pigment are of the latter colour-history. The new points 

 that emerge are the absence of red pigment in certain 

 broods, and its presence in only a percentage of others. 



Repeated attempts were made to experiment with broods 

 from an isolated parent under diverse conditions of light, 

 food, and temperature, but without much success after the 

 first week or ten days. The chief results obtained were 

 (1) that zoese developed and hatched in darkness (from brown 

 parents that became green under these conditions) possess 

 the normal pigmentation, thus showing that light is not 

 essential to pigment development, and also confirming the 

 suggestion just made, that it is those green parents which had 

 been previously brown that give rise to larvte with red pig- 

 ment ; and (2) that there is a steady increase in the amount 

 of red pigment in broods of green parents. For example, the 

 tint of zcea3 of green parents approximated after a few driys 

 to the colouring of the larvae of red parents. It is, there- 

 fore, doubtful Avhether the initial differences in pigmentation 

 between the broods of similarly or diversely coloured parents 

 are of any moment in determining the ultimate coloration. 



III. (1) The Influence op Transmitted Monochkomatic Light 

 ON the Formation op Pigments in Hippolyte Variaks. 



Previous work on the influence of monochromatic light 

 (1900, p. 619, 1904, p. 356) upon Crustacea concerned itself 



