Introduction to Animal Morphology. 2 1 1 



secrete the tube in which the worai lives. The mucous 

 glands of the clitellum in earthworms secrete a chitinous 

 material, like that of the cocoon glands of leeches. The 

 sub-dermal layer may be nucleated protoplasm (Chastonotus), 

 simple, parallel, non-nucleated fibres, unstriped or striped, 

 longitudinal and circular ; sometimes each fibre has a cortical 

 and a medullary layer (Nephthys). The longitudinal fibres 

 are divided into tracts by dorsal, ventral, and lateral lines. 

 Oblique fibres cross from the neuropodia to the notopodia. 

 Deep processes of this layer form septa, dividing the body 

 cavity into metameric chambers, except at the front end, 

 where the first few segments have no partitions. In Polyoph- 

 thalmus, two longitudinal septa, below and free from the di- 

 gestive tube, attached to the medio-ventral and lateral lines, 

 cut off two long chambers from the general body cavity. 

 Direct openings into the body cavity exist in Lumbricus and 

 Enchytraeus. 



The mouth opens on the peristome, and may have 

 a protrusible, cylindrical, club-like or leaf-like epi- 

 pharynx or proboscis, with a boring spine in some 

 Syllidse. The mouth may have 1-5 toothed jaws, 

 often with hooks at the base, and the peristome may 

 have papillae or tubercles. The oesophagus has some- 

 times simple salivary glands, and may dilate into a 

 muscular proventriculus, in which may be chitinous 

 teeth (Gnathosyllis) and glands. The digestive canal 

 is rarely divided into stomach and intestine, coiled in 

 Chloraema and Pherusia. It often has lateral cseca in 

 each metamere, simple or branched, with terminal 

 glandular pouches (Aphrodite). The intestine has, as 

 in Gephyrea, epithelial, basement, and muscular coats 

 (the last transversely striped in Phreoryctes). The 

 middle tract of the intestine may have a lining of 

 yellow or green hepatic cells, but has never separate 

 glands. In the lowest part, gland cells containing 



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