THE (XELOM. 55 



the caeca, are given ofi. They slope more and 

 more backwards as we pass down, and the two 

 last are parallel and contiguous to each other, 

 and to the intestine which lies in a dorsal groove 

 above them. 



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 



dilatation immediately behind the crop, lying be- 

 tween 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 

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

 wall. 



B. The Ccelom. 



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 prin- 

 cipal channels are of two kinds, some having muscular,, 

 others non-muscular walls. Both sets of tubes are parts of 

 the original body-cavity, or ccelom, which is in some kinds of 

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

 of canals the two lateral ones of which have acquired mus- 

 cular walls. There are no true blood-vessels. 



The arrangement and relation of these sinuses are best 

 determined by the microscopical examination of sections, 

 and will be described later on ; the broad features, most of 



