THÉEL, THE AMOEBOCYTES BY ECHINODERMS. 19 



bråte blood. Thus the degree of brightness of the fluid is 

 dependent on the more or less abundant occurrence of the 

 blood-corpuscles. In fact, the intensity of the red coelomic 

 fluid is most striking in Cucumaria elongata, which is in pos- 

 session of an abundance of coloured cells. Next in order 

 comes Cucumaria hyndmani, thereaft^ Thyone fusus, and 

 at last Mesothurin intestinalis, in which a shade of colour 

 scarcely can be perceived. 



A quaintness to be taken into consideration, too, is the 

 individual fluctuation of the blood corpuscles, these being 

 superabundant in some specimens, but fewer in others. I 

 must admit that I am unable to give any reason for this taking 

 j)lace. Another niarvellous matter to think över, concerns 

 the proportion between the coloured and colourless corpuscles. 

 In the event of the red cells being present in great numbers, 

 the white ones become in minority, and vice versa. Con- 

 vinced that they do not develop the one from the other, the 

 matter remains a mystery to me. 



When viewed one by one the coloured corpuscles do not 

 appear red, but merely of a påle yellow tinge; a distinct red 

 colour is produced only when a number of them is brought 

 together. Sometimes, for inst. in some specimens of Thyone 

 fusus, the whole water-vascular system is of a high red colour 

 from crowded red cells, while its coelomic fluid is almost 

 colourless. The blood-corpuscles present themselves under 

 somewhat different forms: in general they are more or less 

 flattened, elongated, oval, or even discoidal. 



Thyone fusus. 



The red corpuscles are commonly not present in such 

 a number in the coelomic fluid, that they can give to it a tinge 

 of colour, whereas they often fill up the water-vascular system 

 to such a degree, that it acquires a high red colour. 



By microscopic observation of the corpuscles just removed 

 from the animal, we can easily state that they are discoidal 

 or oval, flattened and more or less distinctly biconvex (pl. 5, 

 figs. 11 and 12). Their magnitude differs considerably even 

 in the same animal, the largest measuring up to 32,30 \l in 

 diameter and the smallest 15,2 \l, and every gradation in size 

 between these extremes may be met with. Their protoplasm 

 is almost homogeneous, slightly troubled, and lodges one or 



