THÉEL, THE AMOEBOCYTES BY ECHINODERMS. 27 



tion-products in my preparations depend, to some extent, 

 on a stream of water and fixatives drawn between cover and 

 slide. 



Crystals or spicules in coelomic amoebocytes. 



To my knowledge Semper^ alone has dealt with the cry- 

 stals in holothurids. On page 127 of his standard work on the 

 holothuridea from the Philippine Islands, he described them 

 as follows: »Ausser den gewöhnlichen sich stark bewegenden 

 Schleimzellen und den verästelten Zellen, habe ich in drei 

 Fallen noch eigenthiimliche Krystalle haltende Zellen gefun- 

 den. Bei Thyonidium cebuense und Cucumaria canescens fand 

 ich sie ziemlich häufig in der Leibeshöhle, bei Holothuria co- 

 luber dagegen ausschliesslich in dem langen Geschlechtssinus, 

 sodass ich eine Zeitlang fast glaubte, in diesem letzteren eine 

 Niere zu erkennen. Die Krystalle sind immer in kernhaltigen 

 Zellen eingeschlossen, die in Grösse mit den gewöhnlichen rund- 

 lichen Zellen iibereinstimmen ...» 



From this statement, one has a right to presume that 

 Semper considered the crystalliferous cells as different from 

 the plasma-amoebocytes, though it is not clear, whether 

 he means that they are entirely distinct from the amoeboid 

 cell-type, or not. As for myself, I think it most likely that 

 they ought to be enrolled among the true plasma-amoebocytes, 

 though they are dissimilar as to their functional manifestations, 

 and consequently, too, as to their chemical constitution. It 

 is not unlikely that their quality of taking up a superfluity 

 of inorganic salts from the surrounding medium has influenced 

 the cells, their power of amoeboid movements having been 

 suppressed or limit ed. Repeated studies ha ve lead me to more 

 positive consequences. 



From several indications it may be understood that 

 the mother-cells of the crystals belong to the amoeboid type. 

 For it can hardly be conceived, how such singular and charac- 

 teristic crystals, or rather spicula, as those, for inst., in Psolus 

 phantapus can originate without presumption of amoeboid 

 movements of the mother-cells, their pseudopodia shooting 

 out in predeterminate directions and giving rise to the char- 



^ Reisen im Archipel der Philippinen, Th. 2, Bd. 1, Holothurien. Leip- 

 zig 1868. 



