ANIMAL CHLOROPHYLL 363 



in an octopus, and of Bert (1867), who gave an interesting 

 description of the epidermal circulation. Eabuteau and 

 Papillon (1873) obtained a pigment from Octopus vulgaris 

 which failed to give absorption bands. The classic researches 

 on this form, however, are those of Fredericq (1878), who was 

 the first to demonstrate the presence of a respiratory pigment 

 (on haemocyanin, see below) in the blood. In addition to 

 the haemocyanin he found in the blood a red lipochrome. 

 Though there is no direct proof (as there is in the case of the 

 red lipochrome found in the blood of crustaceans) that the 

 substance is identical with the red pigment in the chromato- 

 phores, it is highly probable that such is the case. The colour 

 itself strongly suggests the similarity, while the fact that similar 

 pigments are found in the blood of other animals as well as 

 in their chromatophores, gives added evidence that the two 

 pigments are identical. The best description of the chromato- 

 phores in Octopus is that of Gowdry (1911). 



The inky fluid of the cuttle-fish Sepia officinalis is 

 a pigment which is chemically identical with certain melanins 

 of the higher animals (Piettre, 1911 h). Though melanin-like 

 substances have been reported in gorgonian stems and in 

 certain mollusc shells, their identity with vertebrate melanins 

 has never been proved. Consequently it is a very curious fact 

 that the invertebrate which possesses the most highly organized 

 nervous system should also possess melanin, which in the higher 

 animals is so intimately connected with the nervous system. 

 The question of the origin of melanin and of its chemical 

 constitution will be considered in a later section. 



(c) Other Mollusca. 



Many detailed investigations have been made on the respira- 

 tory pigments of the mollusca, but since these pigments seldom 

 function in the production of coloration, they will not be con- 

 sidered in detail. 



Haemocyanin. — The substance responsible for the blue 

 colour of the blood of certain mollusca was first isolated and 

 described by Fredericq (1878). Haemocyanin has since been 



