III.] 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 

 circuDKESOphageal vessels, connecting the supra-intestinal 

 and supra-neural trunks and sometimes termed pseudo- 

 hearts; secondly, a pair of lateral (Esophageal 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 oeso- 

 phagus and its calciferous glands. A condition somewhat 

 exceptional in the animal kingdom is met with in the blood 

 vessels of the clitellum^ and less conspicuously of the body- 

 wall generally ; where the superficial capillaries pass up 

 and ramify among the actual epidermal cells themselves, 

 giving rise to an epider?Jial 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 sixe, being usually about 

 the 37jo(jth 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. 



