THE CCELOMATA INVERTEBRATA 175 



being folded into the cavity to make a very large ridge-like swelling, 

 the typhlosole, running the whole way down the intestine. It is 

 lined by entoderm, most of whose cells are ciliated, but there are 

 also scattered in it, particularly on the typhlosole, glandular cells 

 which secrete the digestive fluids. The intestine corresponds 

 functionally to both the stomach and intestine in the higher animals. 

 The outside of it is covered and the interior of the typhlosole is 

 filled with large granular cells of a bright golden yellow colour, 

 causing the intestine to stand out in a striking manner. These 

 chloragogen cells, glandular though they are, are not concerned with 

 digestion, but with the excretion of waste nitrogenous matter, as 

 we shah 1 see later. 



The earth in front of the worm containing decaying organic 

 matter, its food, is sucked in through the mouth by the action of the 

 pharynx, and is passed on by a series of waves of contraction which 

 travel slowly down the gut one after another, a movement termed 

 peristalsis. The earth is thus passed through the oesophagus, where 

 the acids in it are neutralised by the calcium carbonate from the 

 calcareous glands, which may also serve for ridding the body of 

 excess of lime salts. In the gizzard it is ground up, and in the 

 intestine it undergoes most of its digestion and absorption. The 

 proteids are turned into amino-acids, the starches to sugars, and so 

 on, and the soluble products pass by dialysis through the intestinal 

 wall into the adjacent blood-vessels to be distributed to the various 

 parts of the body. The insoluble matter from the food and all the 

 earth is passed out of the anus, forming the " casts " already 

 referred to. 



Between the gut wall and body wall the ccelom is filled with a 

 colourless watery matter, the ccelomic fluid, which, as the animal 

 contracts and twists about, is driven backwards and forwards 

 through the perforations in the septa. Thus is set up a very 

 rudimentary circulation which may also help in the conveyance of 

 food, and the fluid may at times exude in tiny drops through the 

 dorsal pores. The plasma of the ccelomic fluid contains two 

 varieties of corpuscles ; in the first place large immobile spherical 

 cells containing many large granules, and in the second typical 

 active amcebocytes with a finely granular protoplasm. 



For the first time in the animal series we encounter an 

 animal that has a definite circulatory system and blood ; for such is 

 present in Lumbricus, in addition to the moving ccelomic fluid. The 

 blood-vessels are a series of tubes rendered conspicuous by the bright 

 red blood within them. The blood owes its colour to Hcemoglobin, 

 which, however, is not found confined to red corpuscles, as in Rana, 

 but is in solution in the plasma. Corpuscles are indeed present, 



