ON COLOURING MATTERS OF VARIOUS ANIMALS. 3 



water, glycerine, alcohol, and ether, also in strong solu- 

 tions of ammonia or potash, and it is not affected by picric 

 acid. When treated with moderately strong hydrochloric, 

 nitric, or sulphuric acids the colouring matter is dissolved 

 and yields on addition of water or alcohol a solution of a 

 peculiar pink colour, which is markedly dichroic, appear- 

 ing green in certain lights. This acid pink solution yields 

 when very strong a broad intensely black band, Avhich in- 

 cludes the D line, and which is continued towards the violet 

 end of the spectrum as a less intense additional shading. 

 When the solution is slightly weakened a narrow interval of 

 light divides the black band into two (PL I, fig. 3 b), and 

 when it is still further reduced in strength the interval 

 between the bands becomes wider ; the more infrangible 

 band becomes much more intense than the narrower one on 

 its red side, and the fainter shading on the violet side of the 

 more refrangible band is lost (PL I, fig, 3 c). When the 

 solution is very weak indeed one band only, the more re- 

 frangible of the two, remains. On addition of alkalies to 

 the acid alcoholic solution the colouring matter is precipitated 

 as a dark burnt sienna-coloured flocculent deposit which 

 yields the original three-banded spectrum of the fresh sub- 

 stance, and is redissolved by acids. The precipitate can be 

 separated by a filter and the colouring matter thus obtained 

 in the pure condition. When dried it appears as an amor- 

 phous brown powder, which appears to have all the proper- 

 ties of the recent colouring matter. 



Polyperythrin was first observed in a species of Cerato- 

 trochus (C diadema, n. sp., H. N. M.), which was dredged 

 on July 10th, 1873, between the Azores and Madeira. It 

 appears to be constantly present in various species of the 

 genus Flabellum, and gives the red tint which is present in 

 the calcareous corallum of many of these, and which is un- 

 impaired by maceration of the corallum in strong caustics. 

 A large series of Flabellum variabile (Semper) was ob- 

 tained by the Challenger in the Arafura Sea in 60 fathoms. 

 Some of the corals had their soft tissues uniformly coloured 

 of a dark madder. In others the colouring matter was 

 present only in more or less marked streaks, whilst very many 

 specimens were entirely ^devoid of pigiment, and of a uniform 

 white, in fact albinos. 



In most of the specimens the corallum was tinged with 

 the colouring matter, but in some it was pure white. 



Polyperythrin has been observed in the following Coe- 

 lenterata. 



Ceratotrochus diddema, dredged off Pernambuco, Brazil, 



