42 THE LEECH 



are much larger than any of the others, extending 

 backwards through several somites, and lying along- 

 side the intestine. 



The crop and its diverticula have their walls thrown 

 injiO very numerous folds, projecting internally. 



Slit up the crop along the mid-dorsal line, wash out its 

 contents thoroughly, and pass a seeker into the several diver- 

 ticula on one side, slitting them open along their whole length, 



6. The stomach is a small spherical slightly bilobed dilata- 



tion immediately behind the crop, lying between the 

 basal portions of the backwardly directed last pair of 

 diverticula, and opening behind into the intestine. 



It is probable that absorption of the food takes 

 place entirely iii the stomach, and its small size will 

 explain the very slow rate at which this absorption 

 is effected. 



7. The intestine is a narrow straight tube running from the 



stomach to the anus. Its inner wall projects as a 

 spiral fold into the cavity. 



Slit open the intestine with scissors along the mid-dorsal 

 line ; loash it thoroughly, arifl note the spiral folding of its 

 wall. 



B. The Ccelom and the Blood-vessels. 



In the leech there is no obvious body-cavity, the space 

 between the integument and the alimentary canal being filled 

 up by muscle, connective tissue, and other structures. 



A complicated system of tubular channels runs through all 

 parts of the body, and is filled with a red fluid, the blood, 

 which contains numerous colourless corpuscles. The principal 

 channels are of two kinds, some having muscular, others 

 non-muscular walls. Professor Bourne has shown that the 

 former are to be regarded as the true blood-vessels, and the 

 latter, which may be spoken of as sinuses, as parts of the 

 body-cavity or coelom, which was originally more extensive, 

 but has become reduced to a system of canals which have 

 acquired secondary communications with the blood-vessels. 



