194 ANNELIDA. 



reception of fluids taken in by suction : the stomach indeed, with 

 the numerous lateral appendages opening from it on each side, 

 would seem to fill the whole body ; and, being extremely dilatable, 

 allows the animal to distend itself to a wonderful extent, so that 

 it is not unusual to see a leech, when filled with blood, expanded 

 to five or six times the dimensions which it presented in an empty 

 state. 



The stomach itself (Jig. 80, 1, A, i,) occupies about, two 

 thirds of the visceral cavity ; on opening it, as represented in the 

 figure, it is seen to be divided by delicate septa into nine or 

 ten compartments, which communicate freely with each other. 

 In each compartment we observe two lateral orifices leading into 

 as many wide membranous pouches (&), which although shrunk 

 and flaccid when in an undistended state, as they are seen in the 

 figure, are easily filled with fluid introduced into the stomach, and 

 are then swelled out into very capacious bags. Perhaps the sim- 

 plest way of obtaining a correct idea of the relative sizes and 

 general arrangement of these organs, is to make a cast of their 

 internal cavities when in a state of distension ; this is readily 

 effected by placing a dead leech in warm water until it is slightly 

 heated : in this state the pipe of a small injecting syringe can be 

 introduced into the oesophagus so as to fill the stomach and cseca 

 with common wax injection ; and, if the body be immediately re- 

 moved into a vessel of diluted muriatic acid, the soft parts will 

 be speedily destroyed, leaving an exact model of the interior. 

 It will then be seen that the lateral caeca increase gradually in 

 size as they approximate the posterior extremity of the body, until 

 the last pair (d) become so large as nearly to fill up the space 

 intervening between the end of the stomach and the anal boundary 

 of the visceral cavity. What is the exact nature of these capa- 

 cious sacs which thus open into the stomach of the leech ? Are 

 they prolongations of the digestive surface, or are they glandular 

 cseca provided for the secretion of some auxiliary fluids poured into 

 the stomach ? These are questions which admit of considerable 

 discussion. On the one hand, there can be little doubt that, when 

 the leech is filled with blood, the various csecal pouches become 

 likewise distended, and they are apparently as well calculated to 

 effect the digestion of their contents as the stomach itself. Those 

 physiologists, however, who embrace a different opinion, support their 

 views by referring to the structure of analogous parts found in other 

 ANNELIDANS : in Aphrodita aculeata, for example, the representa- 



