26 G. HERBERT FOWLER. 



two halves by the fusion of these septa than to regard the two 

 chambers thus formed as special pits for the reception of the two 

 longer mesenteries (10), since they are simply downward continuations 

 of the conical ccelenteron, and mesenteries other than the two 

 longer ones are sometimes attached to their sides. Other details 

 of the skeletal structure do not especially bear on the anatomy of 

 the polyps. 



II. Anatomy. — As was shown by Professor Moseley, Seriatopora 

 is undoubtedly a Madreporarian, and is even more in accordance 

 with the normal types than could be inferred without the aid of 

 sections. 



The whole of the colony is clothed in the customary body wall of 

 ectoderm, mesogloea, and endoderm (Fig. 9), which is supported on 

 the echinulations of the coenenchyme (vide supra, p. 19). The space 

 between body wall and theca is broken up by these spines into a 

 superficial series of canals (Figs. 9, 10, 13), which ramify over the 

 coenenchyme and place the polyp cavities in communication with 

 each other, but do not, of course, extend into the corallum in the 

 manner characteristic of the Perforata, The body wall is continuous 

 with the mouth disc, and from the centre of the latter rises a slight 

 hypostome, through which opens the stomatodaeum. This latter is 

 Crucial in transverse section, the longer arms of the cross being in 

 the dividing plane of bilaterality indicated by the axial and abaxial 

 septa (Fig. 10). 



The tentacles, which are twelve in number, being both ectocoelic 

 and entocoelic, are simple evaginations of the ccelenteron, tipped 

 with a terminal swelling, which is a single " battery " of nematocysfcs 

 (Fig. 11). There is, I believe, no instance yet recorded of the 

 occurrence among Madreporaria of the method of tentacular retraction 

 which distinguishes Seriatopora, namely, that of introversion (Figs. 

 12, 13), the tentacles being invaginated in such wise that the battery 

 is still pointed upwards. In Fig. 13 the ectocoelic tentacles are 

 expanded, while the entocoelic are introverted, a condition not un- 

 common in my specimens. Probably owing to the minuteness of 

 the polyp, no special muscular apj:>aratus for effecting this retraction 

 could be detected. 



The mesenteries, which are twelve in number, are arranged in 



