Anafomy and Histology of a Neiv Earthivorm. 55 



and joins the lateral vessel of each side in somite 18. All 

 these lateral branches are, like the posterior part of the dorsal 

 vessel, thickly covered with the brown chloraoogue cells up to 

 the point at which they pass into the body-wall. They are 

 highly elastic, and after being stretched forward to their full 

 extent during systole of the portion of the dorsal vessel to 

 which they are attached, at once become contorted, or partly 

 coiled, when the dorsal vessel again relaxes. The relatively 

 thick chloragogue coating renders them conspicuous objects, 

 although the blood vessel proper is generally very small. From 

 first to last they are free from the alimentary canal. 



The minute gastric branches reach the dorsal vessel a 

 little before the middle of each somite. A close capillary net- 

 work may be seen in the walls of the intestine, which in some 

 of the anterior somites assumes the form of longitudinal 

 sinuses. 



The subintestinal blood vessel is slung by a mesentery 

 from the ventral median line of the alimentary canal, and lies 

 above the ventral nerve chain, passing along the dorsal side of 

 the apertures in the dissepiments. By the dissepiments it is at 

 regular intervals held near the ventral median line of the body, 

 but in the cavities of the somites lies free in wide loops which 

 extend from side to side. A pair of branches is given off before 

 each dissepiment. It is smaller than the dorsal vessel, consists 

 of a single tube, is non-contractile, and is not coated with 

 chloragogue cells. 



The Genital Organs. 



Three pairs of spermathecae are present in Diplocardia. 

 They occur in somites 7, 8, and 9, increasing a little in size 

 from before, are pyriform in shape, with corrugated outer sur- 

 face when not distended with spermatozoa, and each sends a 

 rather thick duct through the body-wall, near the anterior sep- 

 tum, opening, as has already been noted, opposite the inner 

 pairs of setae. Each sac is provided with a small reniform 

 ccecum, closely attached to one side at the point at which the 

 duct leaves the receptacle. They are rather large, sometimes 

 extending up along the sides well towards the dorsal vessel. 



