THE CHROMATOPHORES OF ANIMALS. 125 



trates the substance of the cell and reappears on its lower 

 surface, winding and branching on this surface in a spiral 

 manner in the same way as on the upper. 



The chromatophore may thus be described as a disk 

 lying between a pair of horizontal nerve-plates, consisting 

 of spirally wound fibres and terminal swellings, the two 

 plates being- here and there in communication through the 

 substance of the cell. 



In Amphibia the development of the chromatophores 

 appears to have been almost as little studied as in the case 

 of fishes. The deep pigmentation of the ectoderm in 

 embryos of the common frog supplies some ground, how- 

 ever, for believing that the chromatophores of Amphibia 

 may ultimately be referred to the same embryonic layer, a 

 view which has been defended by Jarisch (28), who main- 

 tains that the chromatophores in the epidermis are modified 

 ectodermal cells. Ehrmann (31) states that the epithelial 

 pigments of the Salamander are deposited by wandering 

 cells. 



The histology of Amphibian chromatophores has recently 

 been studied by Biedermann (29), whose observations are 

 in close agreement with those of Ballowitz upon fishes, and 

 for the most part confirm the earlier statements of Sir 

 Joseph Lister (30). Biedermann compares the movement 

 phenomena of chromatophores with those of Rhizopods, 

 which possess an external sluggish "hyaloplasm" and an 

 internal more fluid "granular plasm". We may, however, 

 refer to Lister's paper for evidence that the streaming 

 movements of the pigment in Amphibian chromatophores 

 are confined to the pigment granules ; the fluid plasm in 

 which they are suspended appears to be left behind in the 

 branches of the chromatophore when concentration of the 

 pigment sets in. Lister adds that the hypothesis which 

 would seem most consistent with the phenomena of expan- 

 sion is that of a mutual repulsion on the part of the pigment 

 granules induced by some agency strongest at the centre of 

 the cell and feeble in the remotest branches of the offsets. 

 Reading this in the light of Ballowitz's recent demonstration 

 of the situation of the chromatophore between two nerve- 



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