NOTE-BOOK OF A NATURALIST. 345 



the change of colour is gradually manifested, the only 

 permanent marks being two small dark lines along the 

 sides ; and it has been argued, from this description, that 

 the reptile owes its varied tints to the influence of oxy- 

 gen. Mr. Houston is also of opiiiion that the change 

 depends on the state of turgescency of the skin ; and Mr. 

 Spittal regards it as connected with respiration and the 

 state of the lungs. Theories upon theories, as varied as 

 the tints which they profess to explain, have been 

 broached to account for these changes ; but, without 

 dwelling longer upon them, let us turn to the solution of 

 M. Milne Edwards, who, in an elaborate paper published 

 in the Annales des Sciences Naturelles, for January, 

 1834, came to the conclusion that the colour of chame- 

 leons does not depend essentially on the greater or less 

 inflation or expansion of their bodies, or the changes 

 which might thence take place in the circulation or con- 

 dition of the blood ; nor on the distance between the 

 several tubercles or granules of the skin ; but, at the same 

 time, he does not deny that those circumstances may pro- 

 bably exercise some influence. He shows that in the 

 skin of these reptiles two layers of membranous pigment 

 exist, one above the other, but so disposed as to appear 

 simultaneously under the cuticle, and sometimes in such 

 a manner, that the one may be hidden by the other; and 

 he insists that everything remarkable in the changes of 

 the chameleon's colour may be explained by the appear- 

 ance of the pigment of the lower layer to an extent more 

 or less considerable in the midst of the pigment of the 

 upper layer, or by its disappearance beneath that layer. 

 That these displacements of the lower pigment do actually 

 occur he proves; and he derives from those facts the pro- 

 bable consequence, that the chameleon's colour changes, 

 not only during life, but that it may vary after death. 

 He also observes, that there is a close analogy between 

 the mechanism which causes the changes of colour in 



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