x PHYLUM ANNULATA 421 



From the wall of the pharynx there run outwards to the body-wall 

 a number of radially arranged bundles of muscular fibres which, 

 when they contract, draw the pharynx backwards, and at the same 

 time dilate it. Behind the pharynx follows a comparatively nar- 

 row tube, the oesophagus (ces.), which extends through about seven 

 segments. At the sides of the oesophagus, in each of the segments 

 ten, eleven, and twelve, is a pair of rounded projections (ces. gl.). 

 The first pair the riesophageal pouches are hollow, and their 

 cavities are in communication with the lumen of the oesophagus. 

 The other two pairs the calciferous glands are thickenings of the 

 wall of the oesophagus, the fluid in the interior of which is milky, 

 owing to its containing numerous particles of carbonate of lime ; 

 the numerous small cavities which they contain are in com- 

 munication with the cesophageal pouches. Posteriorly the 

 oesophagus is ' followed by a rounded thin-walled chamber, the 

 crop (cr.), and this is followed by a very thick- walled chamber, also 

 of rounded form, the gizzard (giz.). From this the intestine (int.) 

 extends throughout the rest of the length of the body to the anal 

 aperture. It is wide with thick but soft walls, constricted 

 opposite the septa, i.e. in the intervals between the segments. 

 Running along the middle of its dorsal surface is a longitudinal 

 fold, the typhlosolc (Fig. 330, typh.), projecting downwards into the 

 lumen. On the wall of the intestine outside the muscular layers 

 and surrounding the intestinal blood-vessels are a number of 

 granular, yellow cells the chloragen cells (hep) : these are specially 

 abundant in the typhlosole. The terminal part, situated in the 

 last segment, is termed the rectum. 



The whole alimentary canal is lined internally by a cuticle, 

 which is thicker in the gizzard than elsewhere, and by a single 

 layer of columnar epithelial cells, the enteric epithelium,. Some of 

 these cells, more granular than the others, grouped in certain 

 regions, more particularly along the typhlosole, are of the nature 

 of unicellular digestive glands, secreting a digestive fluid. Others 

 seem to be specially concerned in the absorption of the digested 

 food. External to this is a layer of connective-tissue. The 

 greater part of the thickness of the wall is made up of muscular 

 fibres, of which there are two layers, an external longitudinal and 

 an internal circular. These layers are greatly thickened in the 

 walls of the pharynx and of the gizzard. 



The Earthworm, like Nereis, has a well-developed vascular 

 system, consisting of blood-vessels with well-defined walls. The 

 blood is bright red, the colour being due to the same colouring 

 matter, viz. haemoglobin, as in the case of the blood of the higher 

 animals, occurring, however, not in corpuscles, but in the liquid 

 part or plasma ; corpuscles are present, but they are colourless. 

 The- main trunks are the dorsal, the ventral, the sub-neural, the 

 two lateral neural, and a series of transverse branches. The dorsal 



