E. NOMUBA : 



1.1- 



a) intermediate in character between the glandular and the ordinary 

 peritoneal cells. This fact seems to me to suggest the probable 

 origin of these glandular cell- masses, but I can not positively assert 

 them to be derivatives of peritoneal cells, for the intermediate cells 

 may just as well be the glandular cells, which have just expelled 

 their secretory granules. 



The septa begin at the intersegment III/IV and are all set 

 transversely to the alimentary canal. In the anterior segments of 



the body the septa are 

 thin, especially septa 

 X/XI and XI/XII, but 

 posteriorly they are 

 more or less thick. 

 Each septal wall con- 

 sists of ordinary, but 

 somewhat flattened 

 peritoneal cells and 

 contains the septal 

 muscle fibres. These 

 are better developed in 

 the anterior septa than 

 in the posterior, and 

 they may be divided into two sets according to their courses (fig. 

 4) : one of semicircularly arranged fibres, which are attached at 

 either end to the body wall on either side of the ventral nerve cord 

 and act by their contraction as constrictors of the main visceral 

 organs ; in the other set the diversely arranged fibres originate 

 from the dorsal and lateral body wall and are attached to the above 

 mentioned semicircular muscle. Each muscle fibre is always divided 

 into two or more branches at their ends. The septal peritoneum, 

 like that of the body wall, is also supplied with blood-capillaries. 



— ^if 1.1 



a.v 



Fig. 4. 



Anterior view of septal muscles from an anterior 

 segment. Reconstructed from sections. xl50. 1.1 — 

 lateral line, a.c — alimentary canal, n.c — ventral nerve 

 cord, d.v— dorsal blood-vessel, v.v — ventral blood-vessel. 



