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



acteristic protrusions of the crystals. The fresh white-shining 

 crystals are always surrounded by a thinner or thicker plasma- 

 layer (pl. 3, figs. 1—5, 8—10 and 21—22). The last figures 

 represent two fresh rhombic crystals with their peripheral 

 plasma-coat sending forth two or three, slightly movable, 

 short and fmger-like protrusions from the acute angles, indic- 

 ating future processes of the crystals. 



When working with the plasma-amoebocytes of Parechinus 

 miliaris I made a provisional classification of them according 

 to their different external appearance in my preparations. 

 Now I think that such a classification is better grounded with 

 regard to the crystalliferous cells, while they are able to exe- 

 cute different structural works. In fact, each crystalliferous 

 cell gives origin to a single crystal of about the same size 

 as the cell itself, thus occupjdng its whole interiör, leaving 

 only a small space free for the nucleus. It is true, too, that the 

 crystals present various forms, not only in different animals, 

 but also many times in the same species. Now, it appears 

 most likely that the mother-cells themselves represent different 

 species or varieties, as to their capability of producing diffe- 

 rent crystals characteristic of certain species of holothurids. 



Among the eight species of holothurids examined, only 

 Labidoplax buskii seems to be in want of true coelomic crys- 

 tals. With few exceptions, the crystals belong to the rhombic 

 system or to derivatives of them. In fresh fluid, all crystals 

 are white, bright shining and refractile. 



Labidoplax buskii. 



As alluded to above, this species lacks crystals in a proper 

 sense, but nevertheless its coelomic fluid contains bodies, the 

 true nature of which still may remain problematical, though 

 I believed them for a long time to be crystals. They occur 

 thinly scattered among other corpuscles and appear in dif- 

 ferent forms. They are hyaline, oval, elongated or fusiform 

 (pl. 1, fig. 2). Their length varies greatly. from 11,4 {x to 30,4 

 \L, and every gradation in size between the two extremes may 

 be met with. Treated with fixatives and stained by Heiden- 

 hain's iron-alum haematoxylin method, the mysterious bodies 

 become dark blue, and their central portion with nucleus (? ) 

 almost black. Pre^uming these bodies being non-crystals, it 

 remains to be revealed what they are? Something like the 



