CALOAllEOUS SKELETON OF THE ANTllOZOA. 521 



seen to be full of eosiiiophilous granules lying iii small vacuoles. 

 At the bottom of the drawing is a sort of loose feltwork of un- 

 stained tissue, which is probably the organic matrix of the 

 coralluui. Minute crystals are adherent to this feltwork, and 

 in places it is covered with minute black granules, wiiicli are 

 invariably present on similar organic remnants in partially de- 

 calcified specimens. To the left are some bundles of acicular 

 crystals of carbonate of lime, broken up by the action of the 

 acid. It appears as if some of the calicoblasts in the figure were 

 in the course of disintegration, and I have observed this break- 

 ing up of the cells not only in many other instances in Helio- 

 pora, but also in many different species of Madreporaria. 

 In the latter case the disintegration is not a result of macera- 

 tion, for it is conspicuous in preparations of Caryophyllia, 

 freshly killed by various methods, in which the remaining 

 tissues were excellently preserved. Though 1 have hunted 

 through scores of preparations with the polariscope, I have 

 never been able to find in Heliopora any trace of the formation 

 of spicules or of crystals within cells, such as may be readily 

 discovered in Alcyonium or Gorgonia. I have specially 

 examined the desmocytes, for I was for a long time inclined to 

 the opinion that von Heider and Mrs. Gordon must be right, 

 and that I should find evidences of spicule formation within 

 these structures. But my results were always negative. The 

 calcareous skeleton of Heliopora is not formed from spicules 

 developed within cells, but is a crystalline structure formed by 

 crystallisation of carbonate of lime, probably in the form of 

 aragonite, in an organic matrix produced by the disintegra- 

 tion of cells which I have described as calicoblasts. 



This view is confirmed by a minute study of the corallum 

 itself In carefully made maceration preparations of hard and 

 soft parts tiie most delicate growing tips of the corallum are 

 preserved uninjured, and in close contiguity to the soft tissues 

 from which they originated. Figs. 22 and 23 are careful 

 drawings made with the camera lucida of the spinous projec- 

 tions at the tips of a growing frond of Heliopora. They are 

 drawn under different magnifications ; fig. 22 shows more 



