ANATOMY OP THE MADREPORARIAN CORAL FUNGIA. 309 



basal surface as in the adult) meet in the centre and fuse 

 together, so that the primitively external corallum is now 

 entirely covered over by soft tissues, and one can only predi- 

 cate its origin from the fact that it is everywhere covered with 

 three investing tissues, the ectoderm, now represented by the 

 calycoblastic layer, the mesoglcea, and the endoderm, to which 

 I have above referred under the name of the skeletotrophic 

 investments. That part of the coelenteron which in Fungialies 

 external to the theca on the aboral surface, is the same mor- 

 phologically as the extra-thecal part of the coelenteron described 

 as existing around the upper part of the calyx in other corals 

 by von Koch, von Haider, and Fowler. For further information 

 on this interesting subject I must refer the reader to the 

 published works of these three authors. 



The Stomodseum. — This is extremely short in Fungia. I 

 was unable to trace the existence of gonidial grooves (siphono- 

 glyphes) at its ends, though they no doubt exist. When alive 

 the animal constantly closes the middle portion of its mouth, 

 leaving small apertures at the extreme ends through which 

 currents of water pass in and out. I did not determine 

 whether these currents are constant in direction. 



Histology. — This is simple in character and does not diflFer 

 in any essential from the Actinian type. 



The ectoderm of the peristome is composed of long columnar 

 epithelial cells, whose inner ends are drawn out into fine pro- 

 cesses which rest on the mesogloea ; each ectoderm cell has a 

 distinct oval nucleus which stains deeply in borax carmine. 

 Numerous smaller interstitial cells lie between the processes 

 of the inner ends of the epithelial cells. Large nematocysts 

 are embedded in the ectoderm ; they are especially abundant 

 on the ectoderm of the tentacles, but excepting for this the 

 histology of the tentacles is quite similar to that of the rest of 

 the peristome. I could not distinguish more than one kind of 

 nematocyst in Fungia. In every case the lower part of the 

 thread is armed with a spiral line of spines ; when inverted the 

 terminal end of the thread is coiled obliquely round the basal 

 portion. The ectoderm of the aboral surface differs slightly 



VOL. XXVII, PART 3. NEW SER. Z 



