254 G. HERBERT FOWLER. 



replace the ejected nematocysts. On the peripheral face of the 

 niesoderm-lamella lie longitudinal muscle fibres continuous with the 

 transverse fibres of the mesentery ; on the central face, oblique fibres. 



The stomatodaeal ectoderm is not essentially different from that of 

 the mouth-disc ; and though there are well-marked gonidial grooves 

 (food grooves, Mundwinkelfurchen), they show no differentiation of 

 ectoderm comparable to that of Alcyonarians (the "siphonoglyphe" of 

 Hickson). 



The whole of the coelenteron is lined by endoderm of cubical or 

 columnar cells ; generally it is only one cell deep, and in the living 

 animal presumably ciliated throughout. At the point where it passes 

 into the thickening known as the mesenterial filament (if that be 

 indeed endodermal in origin) its characters change, and the number 

 of nuclei increases enormously, together with the length of the cells. 

 Its histological appearance entirely bears out what physiological 

 investigation has also shown for the similar filament in Actiniae, that 

 it is secretory in character, producing a proteolytic fluid (fig. 10). 



Nematocysts do not occur apparently in the true mesenterial filament, 

 but only on that portion of it which is continued on to the contorted 

 lamellae, which I regard, in part at least, as equivalent to the acontia 

 of Actiniae. Those occurring on the tentacles are of a different size 

 and shape from those which characterise the acontial filament, though 

 in the latter both forms are found. The smaller, occurring on the 

 tentacles, is -06mm. x -01 mm.; the larger, which is only to be found 

 on the acontial filament, is "1 mm. x -025 mm. The thread of the latter 

 form is covered with minute barbs, which give it, when coiled up in 

 the capsule, a granular appearance. 



Rhodopsammia Parallela (Semper). 



This form, belonging to the family Eupsammidae, affords a very 

 good example of a perforate Madreporarian. Budding sparsely, 

 it forms no ccenenchyme, so that the polyp can be studied easily and 

 without the complications incident to coenenchymatous species. 



i. Of the Corallum the systematic characters have been already 

 described by Semper (12), but certain corrections are to be made in 

 his account relative to the arrangements of the septa. Beautiful 

 figures of the colony will be found in his paper, which contains much 

 valuable and curious information about the group Madreporaria. 



The corallum of a polyp is about 30 cm. in height ; the calyx, which 



