XI 
THE COLOURS OF REPTILES 
241 
chromatophores, comparable to the irritability dis¬ 
played by many leucocytes, which forces the chroma¬ 
tophores to migrate to the surface of the blood¬ 
vessels. This observation affords an interesting 
parallel to those of Zenneck’s, except that in the 
latter case the chromatophores congregated about 
degenerating blood-vessels, and in Loeb’s case about 
living vessels. Loeb considers that the typical 
coloration of the embryo is similarly related to the 
distribution of its blood - vessels. He promises 
further observations on the subject. 
List describes the pigment of the embryos of 
bony fishes as originating from the debris of the 
yolk. It is then taken up by wandering cells and 
carried to different tissues. The relation between 
blood-vessels and pigment cells described by Loeb 
for Fundulus , List describes as universal for verte¬ 
brates. He considers that the surface of the blood¬ 
vessels forms the main track outwards for the 
pigmented leucocytes, which tend continually to 
migrate from the deeper tissues to the epidermis. 
The two investigators do not appear to have been 
aware of each other’s work. 
The interest of these three sets of observations 
is that they all correlate the production of pigment 
and the development of markings with the physi¬ 
ology of the developing embryo, and suggest that 
we may yet be able to similarly explain colour- 
phenomena in general. 
