18 ARKIV FÖR ZOOLOGI. BAND 13. N:0 25. 



Knoll (1893)^ appears, on the whole, to confirm the 

 statements of Cuénot. 



At last, in his »Recherches sur les leucocytes et le tissue 

 lymphoide des invertébrés» Kollman (1908)^ accounts for 

 his investigations of Holothuria nigra, Cucumaria planci 

 and Stichopus regalis. On page 188 he says: »Enfin on trouve 

 chez Holothuria nigra Gm. en tres faible quantité, chez Cu- 

 cumaria planci Mar., en grande abondance, des hématies 

 véritables chargées d'hémoglobine, dont je ne puis rien dire, 

 sinon que ce sont des disques aplatis possedant une mem- 

 brane, nullement amiboides et pourvus d'un noyau de petite 

 taille peu riche en chromatine. J'ai cherché vainement leur 

 origine. » 



From this survey it is shown that our knowledge of the 

 occurrence of red blood-corpuscles in the holothurids is 

 very limited. My own observations may widen, to some 

 extent, our present views of the matter. 



Already in 1906, when as usual I spent my summer va- 

 cation at the swedish biological marine station Kristineberg, 

 I made the observation that the coelomic fluid of Cucuma- 

 ria elongata had a bright red colour approaching to scarlet 

 and similar to that of human blood. Considering that I was 

 unacquainted at that time with the few informations in the 

 literature, where was stated the presence of red blood in ho- 

 lothurids, this discovery was quite a surprise to me. This 

 very day, I keep a very fine preparation from that time, 

 fixed with Bouin's fluid and stained by Heidenhain's iron- 

 alum hsematoxyline method. Låter on I learned that Cu- 

 cumaria hyndmhni and Thyone fusus, too, were provided with 

 red corpuscles, though more scarcely than in the former, 

 and lately, I found that Mesothuria intestinalis, too, was in 

 possession of a scanty number of them. 



Observation shows that the colour of the coelomic fluid 

 and of that of the water-vascular system is due to the pre- 

 sence of hsemoglobin in special kinds of cells, blood-corpuscles, 

 and not to the colouring matter being diffused in the ambient 

 liquid, as is fhe case in many invertebrates. I leave unde- 

 cided, whether the haemoglobin is identical with that of verte- 



^ XTber die Blutkörperchen bei wirbellosen Thieren. — Sitz. Akad. 

 Wiss. Bd. 102. Wien 1893. 



^ Annales des Sciences naturelies. Sér. 9, T. 8, Paris 1908. 



