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. 



