146 Miscellaneous. 



to a bright light, and in direct proportion to the intensity of the 

 light. The opposite is the case with the Stellio, which becomes 

 paler when exposed to the light of the sun. From this M. de 

 Filippi concludes that the passive state of the skin is that which 

 corresponds to the paleness, because M. Briicke has demonstrated, 

 by the aid of irritation by galvanism, that in the Chameleon the 

 active state of the skin corresponds to the pale, and the passive state 

 to the darkened condition. But this hypothesis of the author needs 

 confirmation. 



However, the causes of the change of colour do not appear to be 

 identical in the Chameleons and the Stellio. In the former M. 

 Briicke discovered beneath the epidermis a layer of polyhedric cells, 

 which, when seen under the microscope without the addition of any 

 liquid, present the most vivid colours of interference ; these colours 

 disappear in hquids — that is to say, in substances of which the index 

 of refraction differs less from that of the layer in question than the 

 index of refraction of the air. M. Briicke consequently calls this 

 layer the stratum of interference, and he thinks that the effects of 

 coloration produced by it are due to the same causes as the luminous 

 effects in their laminae, in consequence of the interposition of an 

 extremely thin layer of air between the cells of this stratum. This 

 layer would concur with the combination of two sorts of pigment 

 in the change of colour of the Chameleon. M. de Filippi does not 

 think that phenomena of interference play any part in the changes 

 of colour of Stellio. The scale of colours is besides so restricted in 

 those animals, that the change may be sufficiently explained by the 

 combination of two pigments of which he has detected the existence 

 in the skin — one yellowish white, occupying the superficial regions 

 of the dermis, the other dark, more deeply seated, but capable of 

 covering the former more or less abundantly. If the changes of 

 colour do not occur in young individuals, this is because the black 

 pigment is deficient in them. 



As regards the mechanism of the change of colour, it cannot be 

 compared with that of the chromatophores of the Cephalopoda ; for 

 no muscular fibres are to be found in the layer of the dermis which 

 contains the pigment-cells. It is by the same consideration that 

 Leydig was led to explain the changes of colour of the Tree-Frogs 

 and Tadpoles by the amoeboid contractions of the protoplasm of the 

 pigment-cells. 



In the case of the Stellio, M. de Filippi has recourse to a some- 

 what different explanation. The papillae of the dermis contain in 

 their deeper layers a network of black pigment-cells, which emit 

 processes to the surface of the dermis, above the whitish pigment. 

 The black pigment maybe injected by means of these processes through 

 the superficial whitish pigment, and cause the change of colour. 

 This injection of the black pigment is ascribed by the author, rather 

 hypothetically indeed, to the turgescence of a vascular glomerule 

 which occurs in each dermal papilla. — Mem. delta R. Accad. di 

 Torino, 1865; Bibl. Utiiv. 25th October, 1866, Bull. Set. pp. 198- 

 200. 



