222 PHYSIOLOGY OF THE INVERTEBRATA. 



setting apart of respiratory proteids for abstraction of oxygen 

 from the air. In this way hsemoglobin may have arisen, and 

 although it is usually said that the mere colour of hsemoglobin 

 is of no use, yet the fact cannot be denied that Tnost respiratory 

 proteids are coloured todies. The molecular complexity of the 

 histohsematins is certainly not so great as that of hsemoglobin, 

 and their respiratory capacity is apparently far inferior to 

 that of hsemoglobin, for the histohsematins do not take up the 

 oxygen in a loose coinbination, although they certainly do 

 unite with it in a more stable combination. At the same 

 time, one must remember that the myohsematin or the 

 histohsematin procurable from dead tissues differs in spectrum, 

 and therefore probably in chemical composition, from that of 

 the living tissues. It is well known that no free oxygen can 

 be obtained from muscle, and if myohsematin be the body 

 with which it unites, then myohsematin must certainly have 

 something to do with the storing of oxygen in muscle ; and 

 if this be the case in muscle, it must be the case in other 

 tissues, and in the organs in which the histohsematins are 

 found." 



In studying the chromatology of many Invertebrates, 

 MacMunn "has been struck by th^ fact that while some of 

 their colouring matters can be reduced by such reducing 

 agents as ammonium sulphide, yet by shaking with air, or 

 by passing a stream of oxygen into them, they cannot be re- 

 oxidized ; in this point they afford a parallel to the histo- 

 hsematins. Krukenberg has noticed the same thing, and he 

 has justly concluded that the respiratory processes of many of 

 these animals is not as simple a matter as it is supposed to 

 be. There can be no doubt that the union of these respira- 

 tory colouring matters with oxygen is a much more stable 

 one than is the case with hsemoglobin. It is in the observa- 

 tion of such facts as these that the spectroscope comes to be 

 of value, for if these bodies did not show absorption bands, 

 one could not determine whether they were in the oxidised 

 or reduced state." 



