82 



also explains why sometimes the water vascular system has been 

 considered to play the role of an organ of excretion because 

 it also contained these amibocytes. The importance of this 

 system for respiration can not be doubted, as we shall see in the 

 chapter on respiration, especially not because hemoglobin, 

 whenever it occurs in this group, is found in this very system. 

 I myself could see this once very beautifully in a starfish which 

 had been fed on ammonium carminate ; the whole dissepiment 

 of the water vascular system appeared on dissection to be colered 

 brilliantly red even into the very tips of the arms. 



The well known paper of Kovalevski 75) on organs of 

 excretion in lower organisms, has given rise to a whole series 

 of analogous investigations. This author injected small quantities 

 of a certain dye into the animals to be studied, and observed 

 where it w r ent to. That such organs would have the function of 

 excretion is, however, not necessarily true. On the contrary, 

 the diversity of the results obtained by such methods with different 

 dyes, makes this rather improbable. C u e n o t 23) distinguished 

 between ,,nephrocytes a carminate" and ,,nephrocytes a indigo". 

 These nephrocytes, according to him, desintegrate in the coe- 

 lomic liquid, are taken up by the phagocytes and eliminated 

 through the skin-gills, as described above. 



One fact must however be mentioned as the result of many 

 such experiments, i.e. the frequent accumulation of the injected 

 dyes in the so-called axial organ ') and in the bodies of Ti ede- 

 ma nn. Injecting a suspension of carmine or B i s m a r c k-brown 

 into the water vascular system by means of one of the tube-feet, 

 he found the bodies of Tiedemann stained in the starfishes ; 

 injecting such substances into the coelomic liquid of urchins, 

 he found them in the axial organ. Leipoldt 79) denies their 

 excretory function, pointing out that these organs do not have 

 a glandular epithelium and do not stand in connection with the 

 perivisceral fluid ; furthermore that the current of the stone-canal 

 moves inward. It is rather remarkable to observe here that again 

 we have to do with an organ in the neighborhood of the stone- 

 canal, which should thus be furnished with much oxygen. 



The great objection to all such experiments is that they are 

 ,,unnaturai" and that, though they have given valuable infor- 

 mation in mammalian physiology, they may not have any value 

 in these groups, because we only have to do with a kind of 

 vital staining. The same thing also holds true for many experi- 

 ments on the amibocytes as excretors, especially for the expe- 

 riments of Metschnikoff who made his original studies 

 on phagocytosis on this very group. The fact that the phago- 



!) The axial organ or ovoid gland has been supposed to have excretory 

 function by a great many authors, among which Jourdan, Perrier, Koehler, 

 Hamann, the Sara sin's etc. 



