j52 earthworms, phylum ANNELIDA 



cell. Ihe epidermis of the clitellum consists of several layers 

 of gland cells. Below the epidermis is a circular layer of muscle, 

 consisting of unstriped fibres running around the body, and 

 below this again lies a much thicker longitudinal layer of muscle, 

 composed of similar fibres running along the body and placed 

 in rows which stand at right angles to the surface, supported 

 by connective tissue. On the inner side of the longitudinal muscle 

 is the coelomic epithelium, which is here a layer of pavement cells 

 lining the body cavity. 



NUTRITION 



The ahmentary canal is straight. It begins with a short, wide, 

 thin-walled mouth or buccal cavity in the first three somites, 

 which leads to a muscular region known as the pharynx. This lies 

 in front of the septum between the fifth and sixth somites, but 

 pushes that septum backwards as far as the seventh. When the 

 worm is swallowing soil the pharynx is everted to a length of a 

 few millimetres. Its dorsal wall is thickened by the presence of 

 a number of glands, whose secretion, containing mucin and a 

 ferment which digests proteins, is poured over vegetable tissues 

 while the animal is feeding upon them. Numerous strands of 

 muscle run from it to the body- wall. Behind it lies the oesophagus, 

 a straight, narrow, thin-walled tube, which extends to the 

 fourteenth segment. In the eleventh segment it bears at the sides 

 a pair of oesophageal pouches, and in the twelfth two pairs of 

 oesophageal or lime glands. These contain large cells which secrete 

 calcium carbonate and pass it through the pouches into the 

 oesophagus. In the fifteenth and sixteenth segments the oesophagus 

 expands into a large, thin-walled crop, which in turn communi- 

 cates behind with the gizzard, another swelling, with thick 

 muscular walls and a chitinous lining, in segments 17 and 18. From 

 the gizzard to the anus runs a wide, thin-walled tube known as 

 the intestine. The intestine is narrowed w^here it passes through 

 the septa, and its dorsal wall is infolded to form a longitudinal 

 ridge known as the typhlosole. The gut is lined with a layer of 

 columnar epithelium, outside which are thin longitudinal and 

 circular muscular layers, covered by the coelomic epithelium, 

 which here consists of the chloragogenous cells. These cells, 

 which also fill the typhlosole, are large and contain yellow 

 granules of a substance which is possibly a phospholipid. They 

 '^f into the coelomic fluid, and there break up and set free 



