Januakt 22, 1904.] 



SCIENCE. 



135 



has been possible fairly to distinguish sev- 

 eral classes of such pigments, differen- 

 tiated physiologically as follows: 



1. Those directly serviceable in the vital 

 processes of the organism. Under this 

 head may be classed such pigments as hse- 

 moglobin, chlorophyll, zoonerythrin, chlo- 

 rocruorin and perhaps others less known. 

 It need not be emphasized that by far the 

 most important of these are the two first 

 named. The others, found chiefly among 

 the lower invertebrates, are believed to 

 serve a function similar to the first. 



2. Waste products. Among these the 

 several biliary products are too well known 

 to call for special note. Guanin is a pig- 

 ment of common occurrence in the skin of 

 certain fishes and is associated with the 

 coloration of the species. Similarly cer- 

 tain coloring matters have been found in 

 the pigments of many lepidoptera, known 

 as lepidotic acid, a substance closely allied 

 to uric acid and undoubtedly of the na- 

 ture of a waste product. 



3. Reserve products. Of these there are 

 several series, one of which, known as lipo- 

 chrome pigments, is associated with the 

 metabolism involved in the formation of 

 fats and oils. Perhaps of similar charac- 

 ter are such pigments as carmine, or rather 

 cochineal, melanin, etc. It may be some- 

 what doubtful whether these pigments do 

 not rather belong to the previous class, 

 where should probably be listed such pro- 

 ducts as hajmatoxylin, indigo, etc., all of 

 which have been claimed as resultants of 

 destructive metabolism in process of being 

 eliminated from the physiologically active 

 tissues of the body of the organism. Of 

 similar character is probably tannic acid, 

 a substance well known among plant prod- 

 ucts and involved in the formation of 

 many of the brownish and rusty colors of 

 autumn foliage, particularly of the oaks 

 and allied trees, as are the lipochromes in 

 the formation of the reds and yellows 



which form so conspicuous a feature 

 among autumn colors. 



While the association of these and other 

 pigmentary matters has long been known 

 in connection with both animal and plant 

 growth, and while the conception of their 

 more or less intimate relation to the active 

 metabolism of the various tissues is not 

 new, comparatively little has been done 

 toward directly investigating and eluci- 

 dating the exact nature and extent of the 

 process. This seems to be especially the 

 case in relation to the part played by 

 these products in the formation of those 

 features of coloration among organisms 

 with which we are now concerned. 



The most strenuous advocates of the pri- 

 mary importance of natural selection as 

 the chief or only factor in adaptation are 

 free to admit that among the simplest 

 forms particularly, color has originated in 

 some more or less obscure way through 

 growth or some of the vital activities of 

 the organism, Darwin, for example, merely 

 suggesting that 'Their brightest tints re- 

 sult from the chemical nature or minute 

 structure of their tissues,' and Wallace in 

 the even less explicit statement that 'color 

 is a normal product of organization, ' what- 

 ever that may imply. 



So far as I am aware Eisig was among 

 the earliest to claim that among certain 

 annelids the colors were primarily expres- 

 sions of the katabolic processes of the tis- 

 sues, and were excretory in character. He 

 was able largely to demonstrate this with 

 species of Capitellidee by experimental 

 methods. By feeding the animals with 

 carmine he was able to follow its course 

 through the alimentary tract, its progress 

 through the tissues, and final deposition 

 in the hypodermal tissues beneath the cuti- 

 cle, where in the process of moulting it 

 was finally eliminated. He also found that 

 in a species of Eunice, which fed upon 

 sponges, the pigment granules of the food 



