728 Scientific Proceedings, Royal Dublin Society. 
Though both these specimens contained numbers of embryoes, 
neither of them had attained the full number of the fifth cycle 
of mesenteries. 
In the specimen examined microscopically, the fifth cycle 
seemed to be developing from one pair of directives, where all 
the cycles were complete, towards the other where the fifth cycle . 
was undeveloped. This was not so clear in the macroscopic 
specimen, though the cycles near one pair of directives were all 
complete, while one of the fifth was wanting to one side of the 
other pair of directives. 
Sphincter.—The sphincter is a diffuse endodermal one, being 
merely a thickening of the endodermal muscle lying between the 
marginal spherules and the outer row of tentacles. 
Histology. 
Eictoderm.—There is no cuticle. The nervous layer is every- 
where well developed... The usual gland-cells are present. 
Thread-cells are very abundant in the tentacles and marginal 
spherules; they are scarce elsewhere. ‘The ectodermal muscles 
of the oral disc and tentacles are well developed: these are the 
only places where ectodermal muscle fibres occur. The gullet has 
the usual structure. 
The marginal spherules are placed just outside the sphincter. 
In longitudinal sections they are often irregularly quadrangular, 
the external angle being the most acute. The ectoderm is much 
thicker here than on other parts of the disc. In some sections it 
can be seen to form three layers : 
(a). A layer of delicate fibres with a few scattered small cells. 
(b). A layer two or threerows deep of fusiform granular cells 
very closely set ; there are also a few thread cells and a 
few supporting cells. 
(c). The outer layer, one row of cells deep, consisting almost 
entirely of thick-walled thread-cells set evenly side by 
side; there are also a few fusiform granular cells like 
those of layer (2). At the edges of the spherule, the 
ectoderm is much like that of the disc, only somewhat 
thicker, and with more numerous thread cells. The 
mesogicea and endoderm have the usual structure. 
