io8 Natural History Bulletin. 



entirely, while those near the center will not entirely dissolve 

 even where thin sections of the branch are immersed in a 

 strong solution of the acid. There is no apparent difference 

 between spicules situated in different parts of the zoanthodeme 

 and it therefore seems likely that the action of the acid forms 

 a new chemical compound which arrests the further dissolu- 

 tion of the earthy salts, a result having man}- parallels in 

 chemical action. 



It may also be mentioned that in decalcified sections which 

 I have, spicules may be found presenting ever}' degree of dis- 

 solution from apparently entire specimens to those which are 

 completely dissolved away leaving no discernible residue. 



Fig. lo, PI. I, is a representation of two cells, highly mag- 

 nified, in which a deposition of calcareous salts appears to 

 have commenced; hence, I conclude that these are spicules 

 "in embryo" if I may so speak. A careful study of those 

 cells as well as of the stellate cells illustrated in fig. 9,* PI. I, 

 had led me to regard it as extremely probable that the for- 

 mer are derived from the latter before I found that the obser- 

 vation had already been made by Kowalevski.' 



The derivation of the spicules is therefore mesoblastic. 



It is interesting in this connection to note 



ist. The calcareous spicula of Spoiiges develop in mes- 

 odermal cells. 



2d. We have seen that the spicules of Gorgvnidce have a 

 similar origin. 



3d. That the calcareous spicula in the cutis of the Holo- 

 tlmroidea'^ take their origin in mesodermal cells. 



4th. That the calcareous plates in the Echinoidea and 

 Astroidea are mesodermal in origin. 



5th. That the entire axial calcareous skeleton of all Vo'te- 



1 "It! Sy/n/>odium coralioides, Kowalevf'ky has shown more completely the 

 derivation of the stellate mesoblast cells from the epiblast. He finds that the 

 •calcareous spicula develop in these cells as in the mesoblast cells of sponges." 

 — Comparative Embryology. F. M. Balfour. Vol. I. p. 138. 



2 Idem., pp. 456, 457. 



