CHAMELEONS. 
105 
the Chamaeleon enjoys a pre-eminence which it scarcely deserves. 
For many lizards and other animals possess the same property, 
if not in the same degree. We may mention more particularly 
the cuttlefishes among invertebrates, and among true fishes the 
sticklebacks. A large number of similar instances might be 
cited. 
We must here distinguish changes due to the presence of 
special pigment- cells, or ‘chromatophores/ from diversities of 
colour depending on true variation, sex, age, seasons of the 
year (notably in animals which moult) and the more transient 
results of altered states of the circulation, as in blushing or the 
reverse. 
When chromatophores are present they are affected by 
physical influences, such as light, heat, contact of foreign bodies, 
and other varying external conditions ; they are also subservient 
to emotional causes. 
Chromatophores- occur in several reptiles, batrachians, fishes, 
mollusks, crustaceans and insects. They are deep-seated tegu- 
mentary cells which contain a dark pigment. According as 
they approach or recede from the surface of the skin, they 
modify the tints of the semi-transparent more external layers. 
But how is this movement effected ? It is not the result of 
muscular action, as some have supposed, for the skin has no 
muscles which can thus rearrange its pigment-cells. We hold 
the opinion of Leydig, who is supported by von Siebold, that 
the chromatophores are themselves capable of contraction. 
The contractile substance would seem to be situate chiefty in 
their outer portions. The pigment itself is not diffused but 
granular. It has no inherent contractility, however it may be 
disposed in relation to the true contractile substance.* 
That the nervous system governs the movements of the 
chromatophores may be admitted. Bert, who has made ex- 
periments on Chamseleons to settle this question, asserts the 
presence of two distinct sets of nerves, by which the alternating 
changes of the chromatophores are directly excited. He even 
assigns to these nerves their appropriate centres. But these 
experiments should be repeated. Perhaps they prove too much, 
for we need more positive evidence to disprove the hypothesis 
that the retrocession of the chromatophores is essentially a 
passive movement. 
The opposite sides of the same ChamaDleon may be differ- 
ently coloured. Dead and sickly Chamseleons are paler than 
others. So, likewise, are Chamseleons kept in darkness. We 
cannot follow Bedriaga in his efforts to ascribe the dark tints 
* Harting has made the surprising statement that the peculiar pigment- 
cells of a cuttle-fish (Loligo vulgaris) have a coloured wall enclosing a cavity 
filled with soft contractile protoplasm. 
