346 THÉEL, SKELETON OF THE ECHINODERMS. 



significant part iu the vital processes of animal life. Indeed, 

 they may prove to do so in a much higher degree than science 

 is at present capable to grasp. Metschikoff ^) and several 

 other distinguished investigators have observed that they attack 

 in the main such foreign bodies as have a pernicious influence 

 on the organism. It has also been shewn that they take an 

 important part in the degeneration of various tissues and in the 

 absorption of fatty particles. But the list of their virtues is 

 still not complete. The wander cells not only deposit and form 

 the skeleton in the Echinoderms, but they are also capable of 

 absorbing and destroying it again, thus substituting in the 

 above-mentioned group of animals the orteoblasts and ostoclasts 

 in the vertebrates. They have long been known, it is true, to 

 be calciferous — though there exist some discrepancies with regard 

 to their mode of operation — , but, to my knowledge, their abi- 

 lity to absorb and destroy calcareous particles has only been 

 supposed — never proved — to exist in living animals. 



In my report »On the development of Echinocyamus pusil- 

 lus» I emphasized the fact that the calcareous spicules originate 

 within the calciferous cells in their ectoplasm. Thus, for in- 

 stance, I said: »When the tetrahedron, the first calcareous de- 

 posit of a definite form, makes its appearance in Echinocyamus, 

 I never found it enciosed within the granulär main portion of 

 the cells, hut in the peripheral pseudopodial plasm,^) which has 

 protruded slightly towards the blastoderm, thus appearing as if 



it were placed outside the cells» »But after this is done, 



the formation of the tetrahedron takes place in a clear pseudo- 

 podial plasm situated between these cells and the ectoderm and 

 evidently derived not from one cell but from all the three cells, 

 the pseudopodia of which have united into a small clump». . . . 

 »Thus, according to my opinion, the calcareous tetrahedron is a 



^) In an admirable work »Untersuchungen über die intracelluläre Verdauung 

 bei wirbellozen Thieren» (Arb. Zool. Inst. Wien. T. V. 2 Heft. 1883) he 

 relätes the results of bis researches on the absorption of bacteria and other 

 micro-organisms in the invertebrated animals. 



^) The Italics are my own. 



