CIECULATORY SYSTEM. 45 



backwards through several somites, and lying along- 

 side the intestine. 



The crop and its diverticula have their walls 

 thrown into very numerous folds, .projecting in- 

 ternally. 



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

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

 ticula of 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. 



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 ; wash it thoroughly, and note the spiral folding of its 

 wall. 



B. The Coelom 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. The former are regarded as the true 

 blood-vessels, and the latter, which may be termed sinuses, 

 as parts of the body-cavity or coelom, which is in some kinds 

 of leeches more extensive, but is in Hirudo reduced to a 

 system of canals which have acquired communications with 

 the blood-vessels. 



The arrangement and relations of these vessels and sinuses 

 are best determined by the microscopical examination of 

 sections, and will be described later on : the broad features. 



