ÖFVERSIGT AF K. VETENSK.-AKAD. FÖRHANDLINGAR 1 894, N:0 8. 349 



mals preserved in alcohol. Future investigations may be able 

 to throw light upon this interesting problem. 



Here I avail myself of the opportunity to show that my 

 studies on the embryology of the Echiiioderms have often given 

 me uiisought opportunities of lesuming investigations on the 

 formation of calcareous deposits, and that the results of these 

 repeated investigations seem to confirni the correctness of my 

 former views. The annexed wood-cut represents the odd spicule 

 of the matare plutcus at an early stage in its development 

 surrounded by a thin almost unnoticeable layer of clear ecto- 

 plasm and having the granulär main portions of the cells scat- 



Early stage of the odd spicule characterizing the mature pluteus. The seven rounded heaps 

 represent the granulär main portions of seven oooperating cells which form a kind of 

 ^Plasmodium» their clearer peripheral ectoplasms, into which the spicule is formed and 

 grows, having flowed together and mingled. Drawn from a living larva. Highly magnified. 



tered on its surface. The pseudopodia change incessantly, the 

 first are withdrawn again and others are given out. 



Now I pass över to the process of absorption and to an 

 account of the manner in which the absorbent cells operate in 

 living larvse. In the mature pluteus Avith eight arms and five 

 centres of calcification those rods which support the first pro- 

 truding arms and the hiiid portion of the body appear to be 

 especially well adapted for these studies, because their posterior 

 ends which are easely distinguished early begin to break and 

 dissolve. What follows only pretends to be an explanation of 

 the annexed figures, which present different aspects of the same 

 cells in the state of absorption. 



The cells which effect the absorption and destruction of 

 the larval skeleton are hardly to be distinguished from those 



