310 GTLBEET G. BOURNE. 



from that of the peristome in that the epithelial cells compos- 

 ing it are less columnar and more cubical, and it is scantily 

 provided with nematocysts. 



Between the corallum and the mesogloea there is invariably 

 a layer of rounded, granular, soft-looking cells which do not 

 stain easily ; their nucleus is tolerably large and stains but 

 faintly in borax carmine. From their position these are 

 clearly equivalent to ectoderm cells ; they are the calycoblasts 

 {vide fig. 17, cy.). They are simple rounded cells, as described 

 by their discoverer, von Heider ; I could find no trace of stria- 

 tion in them as Sclater did in Stephanotrochus, nor does 

 their shape agree with his account. 



Between the ectoderm and endoderra of the body wall, and 

 between the two layers of endoderm which form each septum, 

 lies a sheet of homogeneous tissue called by German authors 

 " Stiitzlamelle,^^ by Englishmen " mesoderm," or sometimes 

 " tbe supporting lamina.^' I have called it the Mesogloea 

 for reasons which are more conveniently given at the end of 

 this paper. I could find no trace of structure in this layer in 

 Fungia, though it is possible that the use of proper reagents in 

 the fresh condition might have disclosed a fibrillar structure. It 

 stains slightly with bsematoxylin, not at all with borax carmine. 



The endoderm is composed throughout of a single layer of 

 cubical cells with a tolerably large nucleus and a nucleolus. 

 Presumably these cells bear cilia in the living animal. In 

 many parts of the body, but particularly in the region of the 

 insertion of the mesenteries, the endoderm is crowded with 

 masses of rounded nucleated cells of peculiar appearance ; at 

 first sight they might easily be mistaken for endoderm cells 

 forming a layer several cells deep. When treated with iodine 

 they give a blue colouration, so that there can be no doubt 

 that they are symbiotic algae, which occur so plentifully in the 

 endoderm of many Actinise. I was unable to find any trace 

 of gonads in the specimens which 1 examined. 



The study of the anatomy of Fungia justifies the position 

 which has always been assigned to it, between the perforate 

 and imperforate Madreporarians. The theca, it has been 



