LUMBRICUS TERRESTRIS L. MULLER 93 



region of the intestine, but becomes a thinner and perfectly 

 cylindrical tube in the region of the oesophagus and finally bi- 

 furcates above the pharynx. The dorsal blood-vessel is con- 

 tractile and its pulsations push the blood forward, toward the 

 head. In the other four longitudinal blood-vessels the blood 

 runs from the head backwards and neither of them is contractile. 

 The ventral vessel is the largest among them, although consider- 

 ably smaller than the dorsal vessel. It lies in the mid-ventral 

 line between the intestine and the nervous system and also 

 bifurcates in the region of the pharnyx. The dorsal and ven- 

 tral blood-vessels are connected with each other by means of 

 five pairs of aortic loops or lateral hearts which are simply pul- 

 sating blood-vessels surrounding the oesophagus in the seventh 

 to eleventh segments. The aortic loops push the blood from the 

 dorsal into the ventral vessel. A further connection between 

 the two vessels is established by means of their branches both 

 in the pharyngeal and anal regions of the animal. The subneural 

 blood-vessel runs along the mid-ventral line of the nervous sys- 

 tem. The subneural and dorsal blood-vessels are connected 

 with each other in every segment by right and left parietal 

 vessels, the first pair of which belongs to the twelfth segment, 

 i. e., follows immediately behind the last aortic loop. In the 

 region of the aortic loops the connection between the subneural 

 and dorsal vessels is established through the intervention of the 

 lateral cesophageal vessels. The blood runs in the parietal vessels 

 from the subneural into the dorsal vessel. The last two of the 

 main five longitudinal blood-vessels are the lateral neural vessels. 

 They run at the sides of the nervous system and are connected 

 with the subneural vessel by short transverse vessels of which 

 there is a pair in every segment. The intestinal canal receives 

 the blood supply from the ventral vessel through small intes- 

 tinal branches and the blood returns to the dorsal vessel through 

 similar dorsal branches. The body wall receives its blood supply 

 through lateral cutaneous branches of the ventral vessel. Organs 

 of respiration are absent and the blood is oxidized in the body 



