228 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



segments. They are placed at the posterior margin of the 

 ring which succeeds the second and third chsetigerous 

 annuli. Between the first and second diaphragms 

 there are dorsal and ventral mesenteries* supporting the 

 corresponding blood-vessels ; the dorsal mesentery 

 terminates in front about the level of the posterior margin 

 of the first chsetigerous annulus. The funnels of the 

 first pair of nephridia perforate the third diaphragm, and 

 lie on its anterior face. Behind this diaphragm the body 

 is uninterrupted by septa almost to the base of the tail, 

 but rudimentary septa may be recognised as strands of 

 connective tissue accompanying some of the afferent and 

 efferent vessels connected with the nephridia and gills. 

 Towards the posterior end of the gill region this tissue 

 increases in amount so as to form in the last, or last two, 

 gill segments an almost complete septum. 



It will be seen that all vessels connected with the 

 stomach are attached to its ventral face. This arrange- 

 ment, together with the absence of mesenteries from this 

 region, allows considerable freedom of motion to this part 

 of the gut without endangering the blood-vessels which, 

 by their length and flexibility, appear to readily permit 

 this motion. During digestion the stomach is swung 

 backwards and forwards by movements of the body, and 

 the arrangement of the blood-vessels indicates a con- 

 siderable amplitude of swing. There is, however, a 

 structure which probably acts as a sort of safety cord to 

 prevent the backward motion becoming so great as to 

 rupture the vessels. This is a solid pinkish cord of con- 

 nective tissue, which may easily be mistaken for a vessel ; 

 it is attached ventrally to the anterior wall of the stomach, 

 lies alongside the afferent vessel of the fourth nephridium, 



* The ventral mesentery also runs backwards through a con- 

 siderable part of the third chcetigerous segment. 



