ON COLOURING MATTERS OF VARIOUS ANIMALS. 7 



line band. In a very strong solution, or with weak trans- 

 mitted light, the broad band appears to extend the entire 

 distance from the alkaline band in the extreme red to D, 

 Avhilst the entire violet and blue end of the spectrum is 

 absorbed continuously as far as b. 



By very cautious neutralisation of the solution a green 

 fluid can be obtained, which yields both acid and alkaline 

 spectra showing four bands (PL I, fig. 5 d). In it the ex- 

 treme red band of the alkaline solution and the intense band 

 in the region of D of the acid solution are seen of equal 

 intensity, whilst the second band of the acid spectrum 

 is very faint. In the exactly neutral solution thus yield- 

 ing four bands, acid and alkaline pentacrinin appear to 

 coexist. 



The acid solution of pentacrinin, when slowly evaporated 

 and concentrated, yields a precipitate, which, when collected 

 and dried, appears as a dark violet-coloured amorphous 

 powder. 



This substance, viewed by transmitted light as adhering 

 to the filtering paper, and rendered transparent with glycerine, 

 yields the same spectrum as the acid solution. 



The dried colouring matter is very sparingly soluble in 

 absolute alcohol, but freely soluble in this, on the addition 

 of a few drops of hydrochloric acid. It is not soluble in 

 dilute hydrochloric _acid alone, requiring the addition of 

 alcohol to show the spectrum. 



The fresh colouring matter is soluble in fresh water, but 

 remains partly suspended, forming a slightly opaque dark 

 purple solution, which gives, Avhen quite fresh, a mixed acid 

 and alkaline spectrum- When the aqueous solution is acidi- 

 fied the colouring matter becomes entirely dissolved, and 

 the fluid becomes clear and transparent, and of a beautiful 

 pink, yielding the same spectrum as the acidified alcoholic 

 solution. When the intense watery solution is rendered 

 alkaline a green flocculent precipitate is formed, and in a 

 very intense solution the two outer bands, the most refran- 

 gible and least refrangible, are lost, being encroached upon 

 and included in the general absorption of the ends of the 

 spectrum. 



All the specimens of Pentacrinus obtained off" the Kerma- 

 decs, which were probably of two specicKS, were of a uniform 

 dusky purple colour when brought to the surface, being 

 evidently coloured by acid pentacrinin. 



The specimens obtained off" the Meangis islands were 

 possibly of four species. Of these, three forms were simi- 

 larly coloured dark purple, one being especially dark, whilst 



