V2 



;ni(l hoconiino- a tiiie vessel, runs for the rest of its extent 

 between the ])7'ol)ospis sheath and the intestine. In the 

 intestinal reg'ion the lateral and median dorsal vessels 

 coinnumicate liy a series of commissures (PI. IV., fio-. 1, 

 chr) passinof round the diverticula, and which are of 

 lacunar natuic, hein.o' devoid of the investing laver of 

 ])ai(>nchyinatous cells. As the laleiai vessels do not coni- 

 municale vt'ntially, tlie last coiiiuiissuie (d' the vascuhii- 

 system lies dorsal to the alimentary canal. 



The 1)1 ood is colon iless, and contains some corj)Uscles. 

 Ill some ]N'emeiteans it is icd from the presence of 

 hsemoglohin. As to its course, it has heen stated to How 

 backwards in the median dorsal and forwards in the 

 lateral vessels. It is ])ossil)le, hoM-ever, that, in the 

 absence of contractile fibres in the vascular system, there 

 is no definite circulation, but that the blood is inter- 

 mittently kej)i in motiini by contraction of the mus(des of 

 the body wall. I'o what extent the vascular Huid acts as 

 a respiratory medium is open to (pU'stion. Idie vascular 

 network round the oeso])hag-us of many Xemerteans and 

 the occasional presence of luvmoglobin suggest that it mav 

 have siicli a function, but against this must be set the fact 

 lliai the (esophageal lacume are not present iii some 

 gr(nips, and also that the presence of luemoglobin is of rare 

 occurrence. A more likelv view is that respiration is 

 mainly, if not entirely, carried out by the integument of 

 the smaller forms: and this may al>o be the case even in 

 the larger ones, since the body is usually capable of 

 e.xtreme attenuation. 



i:\(iti;i'()i!'i svsri'.M. 



The so-called excretorv or nepliiidial systejii in Liiniis 

 (/(■ssrri'iis/s consists of a iiumbei- of small tubuh\s lying in 

 close proxiiiiitv to the lateral hicuiue in the (esophageal 



