X] LUMBRICUS 141 



peritoneum (Gr. Trepi, around; TO'VOS, a string). Where this wall 

 adjoins the ectoderm it is called parietal or somatic peritoneum 

 (Lat. paries, an outer wall ; Gr. o-w/xa, body), where it impinges on 

 the gut it is called visceral or splanchnic peritoneum (Lat. 

 viscus-, Gr. cnrXayx vov ) entrail). A septum consists of two layers 

 of peritoneum one forming the hinder wall of the coelomic space 

 in front and the other the front wall of the coelomic space behind, 

 and intervening between the two there is a certain amount of 

 mesen chyme in the form of connective tissue and also channels for 

 the blood. Each septum is pierced with a small hole in the mid- 

 ventral line so that fluid can pass from one coelomic cavity to the next. 



Like all similar spaces in animals the body-cavity of an earth- 

 worm contains a fluid, and in this fluid certain cells float which 

 change their shape as an Amoeba does, and hence are called 

 amoebocytes. As a rule the coelom is completely shut off from 

 the outside world, but in the earthworm it opens to the exterior by 

 means of the dorsal pores (11, Fig. 63), and at times the fluid 

 which it contains escapes through these holes and pours over the 

 cuticle. This fluid has a certain poisonous action on bacteria, and 

 helps to keep the outside of the body clean and free from parasites. 

 Somewhat similar pores leading from the exterior to the body-cavity 

 are found in certain fishes. 



The first segment is divided into two parts, viz. (a) a lip or pro- 

 stomium (], Fig. 62), overhanging the somewhat crescent- shaped 

 mouth, and (6) a peristomium containing the mouth which leads 

 into an oral cavity extending through three segments (Fig. 60). 

 There are no teeth in this cavity and the food is probably sucked 

 in by the action of the muscular stomodaeum, called the pharynx, 

 which succeeds it and reaches back to the sixth or seventh segment. 

 This is followed by the true endodermic tube. The first part is 

 narrow and is called the oesophagus; it reaches to the twelfth 

 segment and has three pairs of lateral pouches developed on its 

 walls. These pouches secrete calcareous particles, and hence are 

 termed calciferous glands. Their formation has recently been 

 carefully investigated by Stephenson and it is interesting. The most 

 anterior pair open widely into the oesophagus of which they are 

 merely lateral dilatations : folds project^into their cavities. As we 

 pass back the free edges of these folos^unite so that the spaces 

 between them form a series of tunnels and these tunnels make up 

 the middle and posterior pair of glands. The oesophagus dilates 

 behind into a thin- walled sac, called the crop, situated in the region 



