286 
ON SUNDRY REPTILES, FISHES, AND MOLUSCJi 
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, Gasterosteus' spinackm.-^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 Fuci. 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 welliknawffhat^TiiradBistfeq 
influence of afiy violent stimulrtS^ "mental or bodily, the larger globuto.'O^Mto# 
will be powerfully and direOtly forced^ into the minutest branches of the vessOli.^ 
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 optica! 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^ 
