198 THE VOYAGE OF H.M.S. CHALLENGER. 



primitive myo- and neuro-epithelia, not so fully differentiated as in the ectoderm. In 

 the Antipathinse the entoderm has a structure which comes closer to that of Cerianthidge 

 than to the condition found in HexactiniaB. This is due to the fact that in Antipathinse 

 the gland cells are numerous, and usually regularly distributed in all parts of the 

 entoderm. 



In Antipatliella subpinnata the entoderm varies considerably in thickness in 

 different parts of the polyp. That of the tentacles has a diameter of 14 to 21 /x ; in 

 portions of the body-wall the layer attains a thickness of 32 /a or more. The 

 entoderm is everywhere chiefly composed of hyaline gland cells, which remain quite 

 transparent in borax-carmine preparations, but in hematoxylin the cell-wall stains 

 slightly. Each cell contains a single deeply-stained nucleus, sometimes placed near the 

 centre, at others near the base. The gland cells vary considerably in shape. Many 

 are subtriangular with one side resting on the base of the layer ; others are broadly oval, 

 whilst others again are more elongate and slender. They vary from 9 to 20 fj, 

 in length, and from 4 to 10 fj. in breadth. The appearance of the entoderm in the 

 tentacles (when stained in borax-carmine) is shown in PL XIII. fig. 8, en ; that of the 

 stomodseum, under similar conditions, in PL XIII. fig. 10, en. In both cases, adjoining 

 the mesoglcea, a thin, granular, or semifibrous layer occurs, in which the bases of the 

 gland cells are imbedded. This probably represents the nervous layer of Actiniaria. 

 Ganglion cells have occasionally been observed at its base ; one of these is represented 

 about the middle of the entodermal nervous layer in PL XIII. fig. 10. Between the 

 hyaline gland cells a number of elongate fibrous cells occur, the course of which is 

 difficult to follow, but they appear to reach the surface of the layer and contain large 

 round or oval nuclei. The hyaline gland cells are frequently so elongate as to reach 

 the surface of the entoderm, or are only separated from it by an irregular layer of cubical 

 cells, each with a large nucleus. In other cases, however, where the gland cells are not 

 so elongate, the surface of the entoderm is occupied by a number of short, ribbon-like, 

 ciliated epithelial cells, which appear to taper below and to be pushed in between the 

 glandular elements. These cells are not well defined in either hsematoxylin or 

 borax-carmine preparations. The gland cells are practically all of the hyaline type, but 

 a small isolated granular gland cell has occasionally been noticed having a similar- 

 position and structure to those of the stomodaeal ectoderm. No nematocysts have 

 been observed in the entoderm. The entodermal muscular system appears to be 

 extremely rudimentary, but a few circular fibres appear to be present in certain parts ; 

 in the greater portion of the layer it appears more probable that the myo-epithelial 

 cells have not given rise to a definite layer of muscular fibres. Borax-carmine does not 

 appear to bring out the muscular fibres clearly ; they have been seen most distinctly 

 in transverse vertical sections of the stomodaeum stained in hsematoxylin. 



Ova. — The ova are contained within dilations of the transverse mesenteries, the 



