KINDS OF COLOR CHANGE 



525 



special nuptial pattern for the breeding period. The changes may be 

 local, as in the spreading of a lizard's throat-fan by engorgement with 

 blood, which then shows red through the transparent skin, or in the blush 

 of an excited macaw, which has a similar basis. But in large numbers of 

 species, relatively rapid changes are made by the whole skin in sympathy 

 with the time of day, temperature, humidity, or the shade or color of the 

 background. Even the nuptial coloration can be put on or off at a mo- 

 ment's notice by some jfishes, such as the cichlids and the red-bellied dace 

 iChrosomus) . These rapid changes were first produced experimentally 

 by Stark in 1830. They are possible because the dermal pigment, or a 

 good part of it, is contained not in inert cells or in defunct or cornified 

 tissues, but in active star-shaped cells. These were discovered and named 



Fig. 157 — Dermal chromatophores of Fundulus heteroclitus; identical chromatophores are 

 similarly numbered in the two piaures. From Parker, after Spaeth. 



a, contracted; h, expanded condition of pigment masses. 



'chromatophores' by Sangiovanni in 1819; and in 1860 Kolliker, study- 

 ing a lung-fish, Lepidosiren, first showed clearly how they work to 

 change the appearance of the animal. 



Only while they are developing do these chromatophores ever actually 

 change their shape. In fully-formed chromatophores, the cloud of pig- 

 ment granules within the cell may be swept into a compact mass by cen- 

 tripetal cytoplasmic streaming, or dispersed uniformly out into the arms 

 of the 'star' by converse movements (Fig. 157). Expansion of the pig- 

 ment masses of a given set of chromatophores gives their particular color 

 (or optical colors which they influence) to the skin region in which the 

 expansion occurs. The aggregation or contraction of the pigment masses 

 makes of them minute dark dots in a pallid expanse of skin, lightening 

 up the animal's coloration or giving some other class of chromatophores 



