LESSON 33.] NUTRITION IN THE ANNELLATA. 



121 



FIG. 



of the other hand, using some pressure at the same time. By this 

 mode of " stripping " the leech, the stomach, and the lateral pouches 

 will be entirely emptied, and the animal soon becomes ready to 

 renew his labors. 



562. Although ever ready to relieve suf- 

 fering humanity of inflamed, or otherwise 

 diseased blood, this does not constitute the 

 natural food of the leech ; it is well known 

 in the sick room that, while the majority of 

 them die from the effects of their first san- 

 guinary meal, those of them that recover re- 

 main in a weakly condition for some weeks 

 afterwards ; and it rarely happens that one 

 leech will do duty a second time. 



5G3. In the sand- worm (Arenicola pisca- 

 torium the fisherman's worm) the blood is 

 of a most brilliant red, and the highly vascu- 

 lar, respiratory tufts, form charming objects 

 (Z, /, Fig. 203), with or without the microscope. 

 The mouth is at a ; the gastro-intestinal 

 canal commences at the termination of the 

 oesophagus (b) by a sudden dilatation, into 

 which two coecal glandular pouches (c) pour 

 their secretion ; the rest of the canal is sim- 

 ple in its outward form, but its walls are 

 thickened by a stratum of minute secerning 

 cells (<?'), which prepare a greenish yellow 

 fluid. 



The circulation of the blood in this worm 

 is very interesting ; there is on each side of 

 the 03sophagus, at its lower part, a contrac- 

 tile sac (/), which sends off a large and 

 short vessel downward, toward the middle 

 ventral line, where, meeting with its fellow 

 trunk, a ventral vessel (e) is formed. This 

 vessel (e) furnishes a pair of transverse 



branches to each ring of the body, which, at the seventh segment, 

 penetrate the branchial tufts (I, I) attached to the sides of that and 

 succeeding middle segments of the body. The pulsations of the two 

 ossophageal ventricles (/) propel the blood into the ventral vessel 

 (e), through the vessels (ra, m) to the gills, where it receives a new 



