Ill ] THE EARTHWORM. 245 



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 

 drcumossophageal vessels, connecting the supra-intestinal 

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

 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 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- 

 sists of a watery plasma in which are suspended exceedingly 

 minute transparent non-nucleated corpuscles. These are 

 somewhat variable in shape and size, being usually about 

 the soVtfth of an inch in length; their structural features 

 agree closely with those of the nuclei of the epithelial lining 

 of the vessels in which they circulate. 



The feature which most clearly distinguishes the red- 

 blood fluid of the worm from that of the Frog, is that its 

 colouring matter is diffused through the plasma and in no 

 way related to the corpuscles. 



