420 



ZOOLOGY 



XKtT. 



r<$ 



circularly arranged fibres (circ. mus.) situated externally, imme- 

 diately below the dermis, and a layer of longitudinally arranged 

 fibres (long, mus.) situated internally. The circular layer is in- 

 terrupted at all the in- 

 tervals between the seg- 

 ments ; the longitudinal 

 layer is interrupted along 

 a series of longitudinal 

 lines, so as to be divided 

 into seven bundles. 



The setae are lodged 

 in sacs, the setigerous sacs 

 (see Fig. 339), lined by 

 a continuation of the 

 epidermis. In the re- 

 gion of the body in which 

 the reproductive organs 

 are lodged some of these 

 sacs are enlarged and 

 glandular, and receive 

 the special name of the 

 cnpsulogenous gla nds. 



The enteric canal 

 (Fig. 331) is, as in 

 Nereis, a tube which 

 runs through the entire 

 length of the body from 

 the mouth at the an- 

 terior to the anus at the 

 posterior end. As in the 

 case of Nereis, it lies in 

 a cavity, the ccelcmc, lined 

 by a thin cellular mem- 

 brane, the peritoneum. 

 and filled with a fluid, 

 the coelomic fluid ', con- 

 taining colourless cor- 

 puscles. It is divided 

 into a series of cham- 

 bers corresponding to 

 the segments by a series 

 of delicate transverse 

 partitions, the septa, or 

 mesenteries, consisting of folds of the peritoneal membrane en- 

 closing muscular fibres. 



The mouth leads into a small bitccal cavity. This is followed by 

 a much larger thick-walled, rounded chamber, the pliai'uru: (ph.). 



