ON CERTAIN GREEN PIGMENTS IN INVERTEBRATES. 405 



of chsetopterin is not very easy to obtain unmixed with chseto- 

 pterin. If the pigment precipitated by marble from an acidi- 

 fied solution be treated with ether, the ether becomes green as 

 already stated,, leaving behind a brownish insoluble residue. 

 If the ether be repeatedly treated with concentrated acid, the 

 acid removes at least the greater part of the chsetopterin, 

 leaving the ether pure green ; the reaction depends on the 

 fact that chsetopterin is more soluble in concentrated acid 

 than in ether ; while the derivative is, on the other hand, solu- 

 ble in ether, but not in strong acid. The spectroscopic exami- 

 nation of the ether usually, however, shows a trace of a baud 

 at X 661, — that is the strong band of chsetopterin, in addition to 

 the band at X641 characteristic of the derivative (see fig, 3). 

 Another method is to treat the precipitate from the acid solu- 

 tion with methylated spirit, and add lead acetate to the solu- 

 tion so obtained. The chsetopterin is precipitated, leaving the 

 derivative in the solution. 



The green derivative obtained in either of these ways forms 

 in ether or alcohol a pure green solution without fluorescence, 

 and giving a one-banded spectrum. On evaporation it is 

 obtained in the form of green oily drops, which are readily 

 soluble in dilute ammonia. It is not soluble in pure water. 

 It was not obtained in large amount, and is apparently formed 

 by the acid splitting chsetopterin into a brown insoluble sub- 

 stance and the derivative : the derivative cannot be recon- 

 verted into chsetopterin. In the absence of detailed chemical 

 investigation this pigment will be simply called the acid 

 derivative. 



(3) Action of Alkalies. 



(a) Ammonia. — The action of ammonia upon solutions of 

 chsetopterin is somewhat peculiar. If a few drops of ammonia 

 be added to the alcoholic solution, there is, as noticed by 

 Professor Lankester in the case of caustic soda, a colour-change 

 to yellow-green without distinct change in the spectrum. If 

 the alkaline solution be allowed to stand for some time, how- 

 ever, the colour becomes a deep pure green with strong fluores- 



