220 PHYSIOLOGY OF THE INVERTEBRATA. 



MacMunn* has discovered various pigments in the tissues 

 and organs of the Echinoderms ; and in most of them the 

 appearances differ in no respect from those seen in Vraster 

 Tt(hens. 



A portion of the tissue or organ is examined in a compres- 

 sorium, by means of which any required thickness can be 

 examined : it is illuminated by a strong light condensed upon 

 it by means of a substage achromatic condenser, and is 

 examined by a microspectroscope (see Fig. 32), or by means 

 of a chemical spectroscope. 



The generative organs ( $ and $ ) and ova of Uraster 

 contain a typical histohsematin. The spectrum of this pig- 

 ment gave the following readings : — 



1st band .... X 613 to X 591, or 593. 



2nd ,, .... X 569 „ X 560. 



3rd X 556 „ X 548-5. 



4th ,, .... X 537 ,, X 516 (about). 



A spectroscopic examination of the stomach-wall and the 

 ampullse of Uraster showed the presence of hsemochromogen. 



" In the integument of Uraster rubens, when it has a, 

 brownish tint, the presence of hfematoporphyrin f can be 

 easily proved, and as the only pigments present in the animal 

 are enterochlorophyll in the radial cseca, histohaematins in the 

 tissues, and a lipochrome here and there, and as hsemato- 

 porphyrin cannot be obtained from enterochlorophyll or from 

 the lipochromes, it is highly probable it is a metabolite of the 

 histohEematins, or, what is less likely, that these pigments may 

 be derived from the same radicle." 



M. Fcettinger states that he found htemoglobin in Ophiactis 

 virens and MacMunn's researches- tend to support Foettinger's 

 idea of the passage from a histohaematin to a haemoglobin. 



* Philosoph. Trans., 1886, pt. i. p. 269; Quarterly Juurn. Micros. Science, 

 vol. 30, p. 5 1 ; Journal of Phxjsiology, vol. 7, p. 242. 



t This pigment can be isolated by digesting the integument in alcohol 

 and sulphuric acid. 



