called the intestine, runs around in opposite direction and parallel 

 to the first. Its festoons alternate with those of the stomach ; 

 in Arbacia they are usually full of faeces. The gut ends by a 

 short rectum, opening into the dorsal anus on a space, called 

 the periproct. Parallel to the stomach and opening into it at 

 both ends runs the so-called ,,siphon" or ,,accessory intestine" 

 (Nebendarm), discovered in 1825byDelle Chiaje. This struc- 

 ture is in some species (e.g. in Dorocidaris papillata, see P r o u h o 

 103)) merely a gutter, comparable to the endostyle of the Tuni- 

 cates, in others a narrow, cylindrical tube lined by cilia. A 

 blood-lacune runs lengthside of this tube (Hamann). In the 

 Regulares it follows the stomach, in the Clypeastroidea it makes 

 a short-cut. Its function is completely unknown, several possi- 

 bilities will be discussed in chapter 21. 



The histological picture of the oesophagus ressembles that 

 of the starfishes very much. Outside of the layer of circular 

 muscles which is also present in tbe pharynx, we find here 

 longitudinal fibres and the ciliated peritoneum, both derived 

 from the lining of the coelomic cavity. The inside layer of 

 connective tissue and circular fibres is often called the visceral 

 or splanchnic part ; the longitudinal fibres plus endothelium the 

 parietal peritoneum. The layer of connective tissue is separated 

 from the epithelium by a very thin, hyaline basal membrane 

 (Hamann). The epithelium of pharynx and oesophagus contains 

 two types of cells : 1 . glandular cells, full of granulae and 2. 

 , t Stiitzzellen", simple supporting epithelial cells. It is about ten 

 to fifteen times as high as all the other layers together. 



Both types of cells are ciliated. The glandular cells are espe- 

 cially frequent in the five corners of the pharynx and in the 

 neighbourhood of the mouth. At their base we find a layer of 

 nerve fibres. The granulae have been studied with much detail 

 by Hamann 51 a ), the same author gives an accurate picture 

 of the act of secretion. In Arbacia we find a pigment present 

 at the outer rim of the cells. 



The first or direct curvature, as the stomach is frequently 

 and more rightly called, shows the same picture except for two 

 peculiarities : 1 . between the layer of connective tissue and the 

 peritoneal lining we find a whole system of lacunar spaces, full 

 of ft lymph cells" ; 2. the cells of the epithelium have almost 

 exclusively the glandular type, all cells are high, ciliated and 

 loaded with granulae of all colors. The first curvature is usually 

 much darker than the intestine ; this is on one hand due to the 

 presence of pigment and secretory granulae in its epithelium ; 

 on the other hand to the blood-vessels which are especially 

 frequent here. This indicates that this part of the gut plays an 

 important role in enzyme secretion and absorption. It also shows 

 many folds, in these folds the glandular cells are especially 

 accumulated (Hamann). 



