ZOOLOGY AND BOTANY, MICROSCOPY, ETO. 37 



now be evident. His other results are: (1) In young cells of the 

 cortical substance of hairs, spines, and feathers, the cell-protoplasm 

 becomes differentiated into fibrils of horny substance, and into an 

 intermediate substance ; (2) the cell-elements of spines are exactly 

 similar to those of hairs ; and (3) the so-called pith of a feather 

 consists of elements of connective tissue, and is nothing more than 

 the dried papilla. 



Distribution of Colour in the Animal Kingdom.* — L. Camerano 

 discusses this subject at length. Colours maybe arranged in accord- 

 ance with the frequency of their occurrence, thus : (1) Brown ; (2) 

 black; (3) yellow, grey, and white; (4) red; (5) green; (6) blue ; 

 (7) violet. Black, brown, and grey are more common in Vertebrata 

 than in Arthropoda, while red and yellow are more generally met 

 with in the lower forms. Green is very frequent in the lower forms, 

 less so in Mollusca, and still more rare in Vertebrata. Violet and 

 blue are the colours most seldom met with, but they occur in all 

 groups of the animal kingdom. White is irregularly distributed, but 

 more characteristic of aquatic animals. The colours of animals bear 

 a relation to the medium in which they live ; parasites are less varied 

 in colour than free-living animals. Aquatic animals are commonly 

 more evenly and less brilliantly coloured than land animals ; pelagic 

 animals, as might be predicted from their transparency, are not 

 strikingly coloured. Among birds, the strongest fliers are most 

 soberly tinted. Of inhabitants of the sea, those that live among Algte 

 are more vividly coloured than those which live under stones or on a 

 sandy bottom ; similarly land animals that inhabit forests are on the 

 whole more conspicuous for their bright coloration than animals 

 which live in deserts. There is no relation between the colour of 

 an animal and its food, as Grant Allen has asserted ; insectivorous 

 animals that live among plants and flowers have often varied and 

 brilliant colours ; on the other hand, herbivorous animals, if they do 

 not habitually live among shrubs and herbs, are dull and uniformly 

 coloured. 



The development of colour stands in no relation to light, but 

 depends far more upon the condition of the animal ; ill-health and 

 insufficient food cause a diminution in the brilliancy of its coloration. 



In very dry climates the colours appear to be darker, while the 

 reverse is the case in damp climates. The various zoological regions 

 of the earth are characterized by a certain dominant range of colour 

 in their inhabitants : grey, white, yellow, and black characterize the 

 animals of the palsearctic region ; yellow and brown those of the 

 Ethiopian ; green and red are the prevailing tints of the neotropical, 

 red and yellow of the Indian region. Australia is distinguished from 

 the rest by the great abundance of black animals. 



In a given group of animals the larger species are usually more 

 uniformly coloured than the smaller. Sexual colours bear a general 

 correspondence to development of the animal ; the males are mostly 

 more brilliantly coloured ; in many cases, however, where the females 



* Zool. Anzeig., vii. (1884) pp. 341-3. 



