SANGUIFEROUS SYSTEM, 



441 



through the transparent body, circulating in the arteries and 

 veins of the common brown coloured erpobdella vulgaris, 

 (133. B ), found creeping on the aquatic plants of our fresh 

 water pools, and guided by eight eyes placed in a curved 

 series along the anterior part of the head, like those of a 

 leech. Here, according to Morren, there are two median 

 vessels, a dorsal and a ventral, (133. B. a,) which, by their 

 waves of pulsation, convey the blood into numerous lateral 

 branches, (133. B. b,) the capillaries of which are continuous 



FIG. 133. 



with those of the two great returning veins, (132. B. c. c,) 

 extending backwards along the sides of the body; the in- 

 ferior median vessel, however, is probably a returning vein. 

 In the prostoma and various other broad forms of pla- 

 nariosj the thin, red coloured serous blood is also observed 

 to be conveyed forwards by the contractions of a single 

 median dorsal artery, and backwards by two lateral infe- 

 rior venous trunks, which present two small vesicular en- 

 largements in their course, analogous to the more numerous 

 minute sinuses seen on the vascular trunks in the lumbri- 

 cus and many other annelides. The planaria viganensis 

 has two minute sinuses on the anterior part of each of 



