232 COLOUR IN NATURE chap. 



hardly be regarded as of excretory nature, they 

 apparently tend to decrease during the process of 

 development, but, on the other hand, they are 

 abundant in adults showing specialised colouring, as 

 in the case of the spotted salamander, and often 

 increase in amount during the breeding season in 

 individuals which exhibit a seasonal change. Reinke 

 {Arch. f. mikrosk. Anat. Bd. 43, 1894) has sought 

 to solve some of those difficulties, and especially the 

 disappearance of the yellow cells from the peritoneum, 

 by the supposition that the yellow pigment may be 

 converted into the black. This is strongly opposed 

 by Fischel, and the question apparently does not at 

 present admit of decisive settlement. It thus seems 

 that the simultaneous existence of both black and 

 yellow pigments prevents us here, as in so many cases, 

 from accepting in its entirety the theory that pigment- 

 ation is the result of an excretory process. 



Although our present knowledge does not enable 

 us to make any statement as to the origin of the 

 lipochromes in Amphibia, yet the developments 

 described above disclose some interesting facts in 

 connection with their distribution. The statements 

 of Fischel and Bedriaga taken together show clearly 

 that in the early stages of development the two sets 

 of pigments are closely intermixed, and that the 

 growth of the larvae or the transition from larval to 

 adult life, tends to be accompanied by a process of 

 segregation, the yellow pigments accumulating at 

 certain spots and the black at others. The process 

 is an interesting one because it seems to occur 

 frequently in birds, in the males as compared with 

 the females. Its external result is to greatly increase 



