ACTION OF CHKOJSiATOPIIOEES. 



93 



with the state that they happen to he in, and differs during 

 contraction and expansion. Heiacke, for instance, has shown 

 that in Gohius Ruthensparri the chromatophores that are yellow 

 or greenish yellow when distended hecome orange-coloured 

 whon contracted ; while the orange or red ones when shrunk 

 become brown or even black. These (so to speak) active 

 movements of the chromatophores were observed before by 

 Lister, whose careful drawings of the chromatophores of a frog 

 have been copied in the accompanying woodcut (fig. 26) ; it is 

 hardly necessary to remark that the studies of the various 



P#* 



FiCr. 26,— CliromatopTiores from the skin of a frog:, copied from Lister, a, wholly con- 

 tracted ; b and c, half relaxed ; d, wholly relaxed ; e, wholly contracted, a capUlary 

 vessel ; /, g, h, expanded colom-cells or chromatophores. 



stages of contraction were made from the chromatophores of 

 living animals, and in fact it is quite easy to repeat these obser- 

 vations on the extended web skin of a frog's foot. 



These chromatophores are distributed in the skin with a 

 certain regularity ; in this particular, reptiles, fishes, and amphi- 

 bians show hardly any — or no — difference. They usually occur 

 in the cutis only, but sometimes they penetrate into the epider- 

 mis, as, for instance, was the case in the section of the skin of a 

 common frog, shown in fig. 25 ; but it is not known whether they 

 then retain or lose their contractility. Sometimes the epidermis- 



