458 ZOOLOGY sect. 



dilate it. Behind the pharynx follows a comparatively narrow 

 tube, the cesophagus (ces), which extends through about seven 

 segments. At the sides of the 03sophagus, in each of the segments 

 ten, eleven, and twelve, is a pair of rounded projections. The 

 first pair — the cesophar/cal pouches — are hollow, and their cavities 

 are in communication with the lumen of the oesophagus (as. gl). 

 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 communi- 

 cation with the oesophageal pouches. Posteriorly the oesophagus 

 is continuous with 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 typhlosok (Fig. 359, typh), projectmg 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 ciliated 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, between 

 which and the external covering of yellow cells are muscular 

 fibres, of which there are tw(j 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. hcemoglobin, 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 j^resent, but they are colourless. 

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

 two lateral neii.ral, and a series of transverse tranches. The dorsal 

 vessi'l (Fig. 359, rfors. v) runs along the middle of the dorsal surface 

 between the body-wall and the intestine ; it is readily visible shining 

 through the former in the living worm. The ventral vessel {vent, v) 



