1906] Animal Coloration. 157 



that which may be distinguished as "Physiological" coloration. 

 Thus the transparent colorless embryo bird acquires a pale pink 

 tint, when red blood first begins to circulate through the rudi- 

 mentary body. Red blood as in the Chironomus larva imparts co- 

 lor, as also does red blood and green blood in many Annelids. Doubt- 

 less the Chlorocruorin in the green blood has a physiological func- 

 tion similar to the Tetronerythrin in yellow sponges. Tetronery- 

 thrin converts oxygen into ozone. Oddly enough it is the subs- 

 tance to which the feathers of many birds owe their orange color. 

 The Gephyrean Bonellia and the Coelenterate Hydra viridis owe 

 their color to minute plant-like bodies filled with green chloro- 

 phyll granules. In many Planarians the same green particles occur 

 and Professor Geddes proved that by them oxygen was liberated 

 as indeed Dr. Joseph Priestley, towards the end of the eighteenth 

 century, had discovered, finding that the carbondioxide in sun- 

 light was broken up and the oxygen given off.* Some colors are 

 " Morphological" or due to features in the anatomy of animals. 

 Many shrimps appear patched with color. A dark patch in the ce- 

 phalothorax is produced by the liver; and their viscera appear 

 as color-masses. The longitudinal dark stripe down the back of 

 the zebra follows the course of the spinal cord, while the white 

 stripes on the (ace of the tiger coincide with the branches of the 

 infra-orbital nerves. 



Closely allied to physiological coloration is that which may be 

 called "Pathological.'" White animals such as white crows, hawks, 

 peacocks, i: moles, eels &c, are abnormal, and known as albinos. 

 Usually the eyes are red owing to the absence of pigment in the 

 retina, as in the rest of the body, though white cats may have 

 blue eyes, are usually deat, as Darwin found out, and as a rule are 

 tom-cats as Lawson stated. A white hedgehog {Erinaceus) i. e. 

 one with the usually brown acuminate spines as white as ivory, was 

 found to lack the normal integumentary nerve twigs. Albinos 

 are evidently abnormal in regard to their peripheral nerve supply. 



* Brandt regards such green particles in animals as parasitic plants in 

 the tissues, or rather commensals supplying oxygen to the host. 



% The surface of the feathers in the white peacock shows the ' eyes ' and 

 usual pattern just as a black horse shows a dappled pattern or glistening 

 spotted appearance. V v a 



