CHESTER. — STRUCTURE OF PSEUDOPLEXAURA CRASSA. 751 



arc columnar, finely <?ranular, with wry small \aciioles, and with a 

 short ciliiim that has a prominent, in\(>rtc(l cone shaped hasal <>;rainde. 

 The nuclei vary from oval to ^lohidar, hut are more often oval, stain 

 lightly, and have one or two prominent nucleoli. The mucus cells 

 (Figs. 30, 37, cl. 7niic.) are columnar or f^ask like, not always reaching 

 the full depth of the layer, sometimes staining evenly with eosin, at 

 other times showing a loose network of protoplasm. This network 

 stains deeply with muci-carmine. The nucleus is in the hasal end, 

 is globular or nearly so, and stains deeply. The granular digesting 

 cells (cl. grn.) are very numerous in some colonies, few in others, and 

 particularly few in starved colonies. They also are columnar or flask 

 shaped with a small round nucleus, that stains lightly, near the middle 

 of the cell. Large granules, staining deeply with haematoxylin, some- 

 times partly, sometimes completel;s' fill the cytoplasm. Nematocyst 

 cells of the smaller type (Fig. 31, cl. nm'cys.') are abundant between 

 the columnar cells in the cilia layer, but the cysts are smaller than 

 those at the surface of the body. They are here nearly globular with 

 a deeply staining nucleus at the lower end. The border, or cilia, 

 region of the supporting cells (Fig. 39) sometimes shows the presence 

 of Aarionsly shaped, but ^ery small, digestive or nutriti^•e granules. 

 Below the nuclear layer and between the supporting cells are found 

 many globular cells (Fig. 30, cl. gl.'), containing large granules that 

 do not stain with haematoxylin. In a few cases these cells have shown 

 karyokinetic figures. I interpret them to be young stages of gland 

 cells and think they are the same as those described by Kassianow 

 (:08). Ganglion cells are found not far from the mesogloea, but they 

 are \'ery few. 



The dorsal filaments and the axis epithelium are described later 

 in this paper. 



Mesogloea. 



The mesogloea is very thin in the body wall of the polyp and in 

 the tentacles, as well as in the stomodaeum and mesenteries. The 

 boundary between it and the ectoderm or endoderm is sharply marked 

 wherever muscle fibers are found; where there are no nuiscle fibers 

 the division is not clear. In the pinnules (Plate 2, Fig. 6) evidence 

 of mesogloea is seldom found, and even in the tentacle (Fig. 5) cells 

 are not often seen imbedded in it. In the stomodaeum the layer is 

 made out with difficulty, but it is thicker than in the tentacles. In 

 the mesenteries (Plate 3, Fig. 33) it is very evident, though thin, 



