162 Investigations mi the Life-History 



solution is saponified by metallic sodium, and in the caustic solution 

 when an alcoholic solution is saponified by caustic soda. 



DISTRIBUTION OF THE PIGMENTS. 



It is interesting to note that the relative amounts of the two 

 pigments vary considerably. As the flesh grows paler, it is the red 

 pigment which seems to disappear first. While the ovary is small it 

 contains chiefly the yellow pigment, while as it increases in size the 

 amount of red pigment also increases. It would thus seem that there 

 is a direct transference of the red pigment from the muscles to the ova, 

 along with the transference of fat. Both pigments occur dissolved in fat. 



SIGNIFICANCE OF THE PIGMENTS. 



In this connection the first point of inte rest is that two pigments of similar 

 or perhaps identical nature occur in the lobster and in all probability in 

 other Crustacea. In the smaller Crustacea, as yet, the red pigment only 

 has been described. In the Crustacea the pigments, especially the red 

 one, are exceedingly important in producing the external coloration. 

 In the lobster the digestive gland contains a considerable amount of fat 

 which has a yellow pigment associated with it. The blood contains a 

 red lipochrome, but no yellow pigment, while the hypodermis contains a 

 large amount of red lipochrome, and apparently a small amount of 

 yellow pigment. The red lipochrome forms a combination with some 

 base, and then gives rise to the blue colour of the shell. 

 (See Jour, of Physiol., 1897, p. 249). There is some reason to believe 

 that in the lobster the yellow pigment and the red are closely related to 

 one another. The yellow pigment contained in the digestive gland is in 

 part got rid of by means of the alimentary canal, where it acts like a 

 true bile-pigment in colouring the faeces, and is probably in part modi- 

 fied to form the red pigment of the hypodermis and shell. 



Now, as to the relation of these facts to the pigmentation of the 

 muscle of the salmon. The most obvious explanation is that the pig- 

 ments of the salmon are derived directly from its food, and this is one 

 which has been made by Gunther, and accepted by other authors, e.g., 

 by Beddard in his " Animal Coloration." At first sight the suggestion 

 has much to recommend it. The pigments are very similar to those of 

 the Crustacea, and perhaps identical with them. They disappear during 

 the period of fasting, and are regained when the animal begins again to 

 take food. In certain brown trout they appear sporadically, as if 

 dependent upon particular diet, and finally the pigments are widely 

 distributed in the Crustacea, occurring in one form or another in fresh- 

 water, littoral and abyssal forms. 



There are, however, some difficulties in the way of the acceptance of 

 this suggestion. In the first place, the salmon seems to feed chiefly on 

 haddock, herring, and similar fish, so that the transfer of pigment can 

 hardly be direct. The herring, however, feeds habitually on small 

 Crustacea, so that it might be said that the pigments of the salmon are 

 obtained indirectly from the herring which forms its food. In consider- 

 ing such a suggestion we have first to remember that the muscle contains 

 two pigments, a red and a yellow, which simultaneously exist in the 

 Crustacea. Of these pigments there is no reason to believe that the 

 red exists in the herring. In three specimens examined I was unable 

 to find any trace of it, either in the muscle or in the viscera. The stomachs 

 in these cases were almost empty, but it hardly seems probable that the 

 amount of pigment in the undigested food of the herring could be 

 sufficient to supply all the colouring-matter of the salmon's muscle. 



As to the yellow pigment, the viscera of the herring yielded to cold 



