OLIGOCH.ITA. 



383 



hypodernris there is present in the clitellus a deeper glandular layer 

 (Sdulenschicht Clap.), which consists of finely granular cells embedded 

 in a framework of pigmented and vascular connective tissue and 

 situated between the hypodermis and the external muscular layer. 

 There are but few setae present, and they are never disposed on 

 special parapodia, but always in simple pits in the integument, by 

 the cells of which they are secreted. 

 There are small secondary bristles 

 which serve as a reserve. The blood 

 is usually red, as in the Hirudinea. 



The alimentary canal is often divided 

 into several regions, the relations of 

 which are most complicated in the 

 Lumbricidce. In Lumbricus, the buccal 

 cavity leads into a muscular pharynx, 

 which is probably used for sucking. 

 This is followed by a long oesophagus 

 extending to the 13th segment, and 

 furnished with a thick layer of glandular 

 cells and several glandular dilated ap- 

 pendages (calcareous sacs). The oeso- 

 phagus is succeeded by a crop, a 

 muscular gizzard, and finally by the 

 intestine itself, the dorsal wall of which 

 is pushed inwards so as to form a longi- 

 tudinal fold, the typhlosole (comparable 

 to a spiral valve). In the Limicolce 

 the alimentary canal is simpler by the 

 absence of a muscular stomach: a 

 pharynx and oasophagus are, however, 

 always present. 



Reproduction. The Oligochceta are 

 hermaphrodite ; they lay their eggs 

 either singly or united in greater num- 

 ber in a capsule; and they develop 

 without a metamorphosis. The testes 

 and ovaries are paired and placed in 

 definite segments, usually near the an- 

 terior end of the body ; they dehisce their products into the body 

 cavity. The generative ducts possess funnel-shaped openings into the 

 body cavity through which the generative products pass, and may 



FIG. 309. Lumbricus rulellus (after 

 G. Eisen) . a, The whole worm ; 

 Cl, Clitellus. 5, Anterior end of 

 the body from the ventral side, c, 

 Isolated seta. 



