116 PROF. A. DENDY AND MR. E. HINDLE : ADDITIONS TO 



showing" indications o£ cilia in places, each cell with a conspicuous nucleus. 

 As usual, it forms a continuous lining to the body-cavity. 



General Structure of Alimentary Canal (fig. 16). — The mouth leads into a 

 wide pharynx supported by the calcareous ring. The pharynx narrows down 

 to a short oesophagus, which gradually increases in size and passes insensibly 

 into the intestine, which is sacculated and slightly convolnted ; but this latter 

 feature may, to some extent, be due to the contraction of the body. It is 

 kept in position by two mesenteries, the anterior one being mid-dorsal in 

 position (d.m.), and the posterior one on the right side. As in all Holo- 

 thurians, the anterior mesentery extends to about the middle of the body of 

 the animal, and is attached to the dorsal side of the alimentary canal and to 

 the body-wall in the mid-dorsal line (d.m.). The right mesentery commences 

 immediately behind the dorsal one, and extends between the right side of the 

 alimentary canal and the right longitudinal muscle, to the posterior extremity. 

 Alono- the intestine run the usual dorsal and ventral vessels. 



Histology of Alimentary Canal. — The epidermis of the buccal region wdthin 

 the bases of the tentacles does not differ from that of other parts of the body 

 except in the absence of sense-papillse and in the presence of large numbers of 

 ciliated depressions, presumably taste-pits, which will be described later on. 

 The buccal region passes gradually into the pharynx, but around the actual 

 mouth is a thicker layer of circular muscle-fibres which probably serves as a 

 sphincter. 



The pharynx is thick-walled and exhibits the following layers from without 

 inwards :— (i-) A layer of peritoneal epithelial cells, (ii.) A very thin outer 

 layer of connective tissue, (iii.) A layer of circularly arranged muscle-fibres^ 

 which is fairly well developed, (iv.) A layer of longitudinal muscle-fibres, 

 (v.) An inner very thick layer of connective tissue in which the fibres are 

 further apart than in the corresponding layer of the integument. It contains 

 a large number of stellate and bipolar connective-tissue cells and a few 

 apparent amoebocytes. Some of the latter are large with deeply-staining 

 granular protoplasm. In addition to these large amoeboid cells, other brown 

 bodies are present which may be either large single cells or aggregates of 

 cells. There is no nervous layer within this layer, (vi.) An inner epithelium 

 lines the pharynx and is composed of elongated columnar cells, tapering 

 peripherally, and covered at their free ends by a hyaline cuticle. Gland- 

 cells occur very commonly between the ordinary columnar cells ; they are 

 much longer than the latter and are rounded off peripherally. They are often 

 arranged around depressions in the epithelium to form simple glands. In the 

 pharynx also occur ciliated depressions (taste-pits) similar to those which 

 are so common in the buccal region. " Sphaeruliferous corpuscles " and 

 wandering-cells are found embedded amongst the epithelial cells. 



