III.] THE EARTHWORM. 245 



having, so far as is known, no direct communication with 

 the body-cavity. The larger trunks of this circulatory 

 system are six in number; median longitudinal supra and 

 subintestinal and supra and subneural vessels respectively, 

 and two small lateral neural ones. These are connected 

 metamerically in a manner described in the Laboratory 

 work (p. 261), and highly efficient capillary systems are 

 established in connection with them. In the segments 

 numbering six to twelve, there exist two sets of vessels not 

 met with elsewhere. These are, firstly, six pairs of enlarged 

 circumcesophageal vessels, connecting the supra-intestinal 

 and supra-neural trunks ; secondly, a pair of lateral oesopha- 

 geal trunks, which are connected with the supra-intestinal 

 vessel in the twelfth segment alone. The latter vessels are 

 specially concerned with the blood supply to the anterior 

 portion of the oesophagus and its calciferous glands. A con- 

 dition somewhat exceptional in the animal kingdom is met 

 with in the blood vessels of the clitellum, and less con- 

 spicuously of the body-wall generally ; where the superficial 

 capillaries pass up and ramify among the actual epidermal 

 cells themselves giving rise to an epidermal blood plexus. 

 The dorsal vessel contracts from behind forwards and the 

 circumcesophageal ones from above downwards; and there 

 is reason to believe that the blood which sets out to the 

 parietes from both dorsal and ventral median trunks, is 

 returned to the vessels of the alimentary system. The 

 exact seat of origin of blood corpuscles during life, to make 

 good the loss of effete ones, is not yet fully determined; 

 but it is highly probable that certain appendages of the 

 blood vessels known as "blood glands" (p. 258) may be 

 concerned in their production. 



The exact seat of respiration in the Earthworm is not fully 

 determined, but there can be little doubt that the red-blood 

 fluid is directly concerned in the process. This fluid con- 



