546 FRANK E. BEDDABD. 



lar bands which occupy a good deal of the coelomic space : it 

 is probable that the reduction of the nephridia in this region 

 of the body is brought about by the development of this exten- 

 sive meshwork of muscles. The septa which lie behind the 

 first are thickened, and formed often of distinct layers of fibres. 

 The last of the thick septa separates Segments 11 — 12; 

 the next septum, however (see fig. 1), although not so 

 thick as those which precede it, is thicker than those which 

 follow. 



A noteworthy point is the non-coincidence of the insertion 

 of the septa with the intersegmental furrows. This frequently 

 occurs in earthworms, but according to Rosa it is possible to 

 trace the fibres belonging to the septum from their apparent 

 attachment to the middle of the segment to their real insertion 

 into the intersegmental furrow. I could not trace any such 

 arrangement in Libyodrilus. The first septum which has an 

 abnormal insertion is 12—13; this and the following six or 

 seven are attached near to tlie middle of the segment just in 

 front of the set£e. It is only dorsally and laterally that the 

 septa are so attached ; ventrally their insertion is quite regular. 

 I have mentioned on page 571 the eflFect produced upon the 

 position of the oviducal pore by the shifting of the interseg- 

 mental septum 14 — 15. 



The principal point of interest in connection with the coelom 

 is the separation of spaces which surround some of the organs. 

 In my description of the vascular system I have referred to the 

 perihgemal space which encloses the subcesophageal blood- 

 vessels ; besides this space, the areas surrounding both of the 

 lateral pair of setae are enclosed by a membrane shutting them 

 off from the general body-cavity of their segments. A series 

 of transverse sections, such as the one illustrated in fig. 19, 

 shows that this membrane is perfectly continuous everywhere, 

 forming a distinct chamber, which is prolonged round the seta 

 sac and nearly reaches the circular muscular coat. In the 

 CapitellidEe Eisig has described somewhat similar lateral 

 chambers, into the floors of which the setae are inserted ; but I 

 am not aware that anything of the kind has until now beeu 



