1882.] Structure, Development, and A ffinities of Phoronis. 373 



be divided into four main divisions, each characterised by a special 

 epithelium : — 



1. (Esophagus. 



2. 1st stomach. 



3. 2nd stomach. 



4. Intestine. 



The transition from the second to the third of these divisions is 

 very marked. The third forms a small strongly ciliated chamber where 

 the gut doubles on itself at the end of the foot. 



The Body-Cavity 



is lined throughout by peritoneum, which passes into mesenteries, 

 dividing the cavity into several chambers. There is a ventral 

 mesentery extending the whole length of the foot, attaching the out- 

 side of both descending and ascending limbs of the alimentary canal 

 to the body- wall. Besides this there are two lateral mesenteries, 

 which pass from the sides of the stomach to the body-wall. By these 

 three mesenteries the body-cavity is divided into three chambers, viz., 

 two anterior and one posterior. The lateral mesenteries end freely 

 before the blind end of the foot is reached, so that all the chambers 

 are here in full communication. 



An important secondary connexion takes place some little way 

 below the tentacles. The intestine attaches itself to the left lateral 

 mesentery, dividing it into two parts, a shorter, attaching the intestine 

 to the stomach, and a longer, attaching the intestine to the body-wall. 

 Throughout the greater part of the foot this results in the posterior 

 of the three chambers being divided into two. 



The body-cavity is further divided by a septum, which passes from 

 the line of the nerve-ring in the body- wall to the oesophagus, into two 

 regions, viz. : — (i,) the space in front of the septum, i.e., the body- 

 cavity in the epistome and the tentacles ; (ii,) the space behind the 

 septum, i.e., the rest of the body-cavity. 



Excretory System. 

 The genital pores discovered by Kowalewsky, by which he observed 

 the ova to pass to the exterior, are the external openings of a pair of 

 nephridia. Each nephridium consists of a simple ciliated tube, whose 

 cell-walls are filled with brown concretions. The tube opens into the 

 posterior chamber of the body-cavity on the sides of the lateral mesen- 

 teries. The external openings are situated in the regions subtended 

 by the anterior divisions of the body-cavity. 



Circulatory System. 



A closed system of vessels, containing nucleated red corpuscles, is 

 present. 



