306 JtR. E. W. li. HOLT ON THE [Apr. 19, 



vessels. Is it simply diffuse d off into the water, or does it bleach 



in situ, and so cease to be conspicuous? The former supposition 



seems to be the more probable, though it is not possible to see any 



trace of it. At present I have no means of applying any test 



other than that of vision, from a want of knowledge of its 



chemical nature. The researches of Gowland Hopkins ' in 



Butterflies suggested to me that uric acid or urea would very 



probably be found in the yellow pigment. With the assistance of 



my friend Mr. F. Bishop Harman, M.B., I made several tests, 



but the results were negative. However, the fact remains that 



the pigment, whatever its exact chemical nature, is, presumably, 



an excretory product and has certain properties of taste and smell. 



It is found only in the skin, and differs entirely in that respect 



from the biliary colouring-matter which I have occasionally found 



infecting all parts of a Teleostean. 



In considering the function of the pigment, it is necessary to 

 note that it is exhibited, by the erection of the dorsal fins, not 

 only in courting the female and in frightening smaller members 

 of its own sex, but also in the attempt, successful or otherwise, to 

 intimidate predaceous fishes. Since the pigment is certainly most 

 abundant at the breeding-season, it may be presumed that it is 

 primarily sexual in function. In this connection it is not easy to 

 decide whether it appeals only to the visual faculties of the 

 female or to her sense of smell as well. The impression I have 

 gathered from repeatedly watching the Dragonets in the aquarium 

 tank and in a large table-tank in the main laboratory is that these 

 fish, in which the olfactory organ is very small, depend almost en- 

 tirely upon their eyesight in feeding. I have often seen them take 

 into their mouths quite uneatable substances which bore a casual 

 resemblance to the worms which form their usual food. To 

 further test the matter I made a decoction of Nereis diver sicolor, 

 the worm in common use here, by pounding up a number of 

 specimens in a little sea-water. The fluid poured off must have been, 

 to the olfactory sense of a fish, identical with the actual worm ; 

 but the Dragonets in the table-tank took no notice of it what- 

 ever. A prawn evidently perceived it, and began to hunt about 

 where some of the suspended particles had fallen. A portion of 

 the same fluid dropped into one of the large aquarium tanks had 

 the effect of rousing a shoal of grey mullet and some red mullet, 

 previously quiescent, to great activity in search of food. It is 

 evident, therefore, that Callionymus is not keen of scent, since a 

 few worms dropped in their tank suflice to bring them from all 

 parts to share the feast. I have not devised any means of testing 

 the effect of smell on the sexual passions of the fish as apart from 

 its appetite, but I can affirm that the yellow pigment is neither 

 distasteful nor terrifying to young members of the species. I 

 made an aqueous solution of the yellow from the dorsal fins of a 

 mature male and soaked in it small balls of cotton-wool, which 



1 Proc. E. S. Ivii. 1894, p. 5, &c. 



