II. Studies in reptilian colour response. I. - The bionomics and physiology of the pigmentary activity of the chameleon

The literature of reptilian colour change extends over twenty three centuries, and yet our knowledge of the physiological processes which govern it, and of the environmental factors which bring it about, is to-day far less complete than for the other two groups of vertebrates which possess pigmentary effectors. The cause of this, it would seem, resides in the fact that the colour changing reptiles inhabit pre-eminently the tropical and subtropical regions of the globe, and are not readily available for physiological investigation in the main centres of scientific progress. The history of this subject is peculiar. From Aristotle to the end of the nineteenth century the literature deals almost exclusively with the chameleon, an animal which for centuries has excited the curiosity of travellers in North Africa, and which, in consequence, has acquired a popular reputation that is quite remarkable. Thus the hundred pages which Fuchs (1914) devoted to reptilian colour response contain far more references to chameleons than to all other reptiles taken together. In the present century, with the single exception of the work of Hogben and Mirvish (1928) from this laboratory, no further investigations on the chameleon have been published. Our knowledge of colour change in reptiles has progressed chiefly through the work of Professor G. H. P arker and his many associates. In the New World chameleons do not exist, and consequently the American workers have turned to other lizards, chieflyAnolis andPhrynosoma . Thus it has come about that most modern workers in this field are relatively unfamiliar with the chameleon, and have tended to overlook the many interesting facts concerning colour change in this animal recorded in the earlier literature