148 PHYSIOLOGY OF THE INVERTEBRATA. 



alcohol, forming a deep yellow solution, giving an ill-defined 

 band at the blue end of the green, beginning to be feebly 

 shaded at about X 526, darker at X 507, and extending to 

 about X 474. On evaporation it left a reddish residue soluble 

 in ether, in chloroform, and other lipochrome solvents, and 

 when in the solid state it became a transient blue with nitric 

 acid, blue, green, and brownish with sulphuric acid, and 

 greenish-yellow with iodine in potassic iodide. Therefore, the 

 blood of Holotliuria nigra contains a red lipochrome like that 

 of certain Crustaceans, as Dr. Halliburton* has discovered," 

 Dr. MacMunn also found this red lipochrome or lutein 

 in the digestive gland of H. nigra; and states that he 

 has no doubt that it " is built up in the digestive gland 

 and carried in the blood current to be deposited in other 

 parts of the body, though what its role may be when deposited 

 there, it is difficult to say. It is not easy to see of what use 

 so much brilliant coloration as exists within the body of 

 Holotliuria nigra can be, except that the lipochrome is 

 changed into some other constituent. If it be respiratory, 

 as tetronerythrin is believed by Merejkowskyf to be, we 

 could see some reason for its existence," but as Dr. MacMunn 

 has repeatedly shown, " what has been called tetronerythin 

 does not exist in two states of oxidation. Merejkowsky 

 would doubtless call the red lipochrome of H. nigra tetron- 

 erythrin without hesitation ; but since he published his results 

 our knowledge of these fat pigments has undergone a change, 

 for we now know that there are a great number of pigments, 

 formerly, with regard to their supposed respiratory properties, 

 included under the name tetronerythrin, which are distin- 

 guishable from each other, and which cannot any longer be 

 called tetronerythrin, the rhodophan of the retina % is not 

 respiratory, nor is the true tetronerythrin in the so-called 

 * roses ' around the eyes of certain birds, respiratory." The 



* Journal of Physiology, vol. 6. 



t Bulletin de la Societe Zoologique de France, 1883, p. 8 1. 

 + Kiihne in Untersuchuvgen a. d. Physiol. Instil, d. Univ. Heidelberg, 

 Bd, I, Heft 4, und Bd. 4, s. 169-248. . 



