286 ON SUNDRY REPTILES, FISHES, AND MOLTJSCA, 



to glide away, never presuming to attack, and being utterly incapable of darting 

 even when assailed. I have killed several of very different sizes, but have never 

 seen one approaching in colour to C. chersea. 



Sea Stickleback, Gasterosfeus spinachia. — Mr. Couch is assuredly correct 

 when he states this little fish to undergo various and rapid changes of colour 

 from the effects of certain passions. Those of fear and hunger are those only of 

 which I have witnessed the influence. 



The G. spinachia swimming about in the deeper pools left by the receding of 

 the tide, is exceedingly voracious, and whenever it perceives and pursues any 

 small fishes, Crustacea or molusca, the variations in tint are immediate, and, 

 from my observation, rapidly returning to the original hue, but, altogether, most 

 amusing to the cautious gazer ; for if the fish but perceives that he is being thus 

 watched, he will forthwith dart away, still varying his hues, into the shelter of 

 some of the densely-interwoven Fieci. What can be the causes of such rapid 

 changes of colour in this fish ? It varies from a dark green to one of a far paler 

 hue, while the sides, nearly of a golden tint, become a clear yellow, or even of a 

 brownish colour, similar to that of the surrounding Fuci. Several other fishes 

 possess similar powers, as the Flounder, some of the Blennies, and two or three 

 of the fresh- water Sticklebacks, inter alia. 



Many reptiles, especially Lizards, nearly rival the Cameleon, certainly in 

 mutability, if not in the quickness of such changes. May it not principally depend 

 upon the alterations which must take place in the excited state of the animal, 

 from the sudden impetus of blood into the very extreme vessels which, by 

 necessarily altering the density of the fine membranes furnished with these 

 vessels, render them wholly and immediately different as media of light, whether 

 transmitted or reflected. Even the size of the particles of such circulating 

 fluids will greatly influence the refrangibility ; and we well know that, under the 

 influence of any violent stimulus, mental or bodily, the larger globules of blood 

 will be powerfully and directly forced into the minutest branches of the vessels. 

 From the structure of those fishes which display such Cameleon-like powers, I 

 should believe this theory to be true, inasmuch as the membranes, though 

 highly vascular and sensitive, are of wonderful tenuity, and susceptible, there- 

 fore, of great and rapid changes, as optical media, from the sudden filling of 

 those blood-vessels by any violent stimulus applied to the heart or nervous 

 system. 



Perhaps, also, the reflected light thrown from surrounding bodies upon those 

 delicate membranous tissues, may produce corresponding alterations in the colour 

 of an animal under peculiar circumstances, and hence will assume a tint very 

 similar to that of the surrounding medium. 



The Gasterosteus spinachia builds a round-shaped nest of marine plants, 



