141 



■gland cells project towards the exterior. The nervous layer 

 is little marked. Over the mesenteries (fig. 6) the 

 appearance is as if the whole had been pressed together to 

 give the enhanced thickness. The rod-shaped nuclei of the 

 layer are closely packed together. The whole is evidently 

 densely ciliated. The outer part is set with large mucous 

 cells, and granular cells extend up from the base. These latter 

 cells are very numerous and lie internally to the layer of 

 nuclei, and, unless actively secreting, do not seem to have 

 processes to the exterior. At the base they are connected by 

 protoplasmic strands to the nerve layer, and in some sections 

 appear to be con nected\vith the protoplasm immediately around 

 definite nervous nuclei. It is characteristic of these gland 

 •cells in this and the next part of the ectoderm to be con- 

 sidered that they usually have their nuclei quite distinct — 

 more or less round with a few granules — and exhibit all 

 phases from rest to active secretion. 



The mesenterial filaments (fig. 8) are presumably 

 ectodermic in origin, as they certainly are in structure. They 

 are of the usual form, a central rounded part (the filament 

 proper) set on the somewhat broadened end of the structure- 

 less lamella. The thickenings of the stomodoeal ectoderm 

 gradually narrow as they pass into the filaments. Allowing 

 for their necessarily constricted base the latter differ in no 

 respect from these thickenings. They have the same thick- 

 ness, the same gland cells and nuclei, the nervous layer alone 

 perhaps not being so well marked. They also seem to be 

 ciliated. On the straight upper edge of the mesentery gland 

 •cells are not so numerous, and the nuclei are very dense. In 

 the central half the whole of the inner part is crowded with 

 granular gland cells, while towards the lower end the fila- 

 ment is more vacuolated. 



Endoderm ffigs. 2, 3, 7 and 8). — Generally cell outlines 

 •could not be distinguished in the endoderm, but in some 

 sections near the attachment of mesenteries the protoplasmic 

 areas had become partially separated from one another. In 

 this position (fig. 2) the layer consisted of low columnar 

 cells with large, flattened, basal processes, spreading outwards 

 •on the structureless lamella. Their nuclei were nearly round 

 with well-defined membranes and network. Between the 

 •cells were a number of large vacuoles, but in this position no 

 glands of any sort could be distinguished. 



More often, except where especially thickened, the endo- 

 derm appears to consist of a vacuolated epithelium of more 

 cubical facies with slightly oval nuclei (fig. 7). In certain 

 positions, where the body-wall immediately overlies the 

 corallum, it is thinner and more homogeneous. On the sides 

 ■ of the mesenteries and under the peristome and tentacles it is 



