PHYSIOLOGY OF THE INVERTEBRATA. 



221 



The integument of Asterias glacialis does not contain 

 hEematoporphyrin, but there is present at least one rhodo- 

 phan-like lipochrome. The radial caeca (so-called liver) con- 

 tain enterochlorophyll and a lipochrome. 



MacMunn has also examined many other species of 

 Echinoderms, and the following table gives a partial summary 

 of the pigments present in various tissues and organs of 

 these animals : — 



MacMunn says that the respiratory proteids " are as im- 

 portant as haemoglobin, if not more so in some animals, and 

 they have the right of priority in time, as they were developed 

 at an earlier period than hsemoglobin, speaking from a phylo- 

 genetic point of view." Even in the lowest of the Meiazoa — 

 the Sponges — MacMunn* has met with histohaematins where 

 they are also capable of oxidation and reduction, and are 

 therefore respiratory. "It is not improbable, but indeed 

 likely, that by a process of physiological selection these 

 respiratory proteids may have become more complex, and 

 their molecular instability therefore greater, as the animal 

 body became more elaborated, and a necessity arose for the 



* Proceedings of Physiological Society, 1886. 



