ON MEGASOOLEX CCERULEUS 73 



received a number of little branches (fig. 7), soon penetrates 

 the intestinal wall. After penetrating the wall both vessels 

 pass on towards the ventral line, receiving numerous branches 

 from the internal capillary network. 



All these dorso-intestinal vessels are formed by the lacunar 

 network^ the anterior pair rather nearer the ventral median 

 line than the posterior pair (fig. 10). 



I have now described all the important vessels in Megas- 

 colex.i 



Course of the Blood. 



Having described all the principal vessels and their relations 

 with one another, I shall now discuss the probable course of 

 the blood, and put forward a theory which is on the whole 

 simpler than any which has been hitherto propounded. 



The reader should bear in mind throughout the description 

 that, according to my theory, so long as the modified anterior 

 extremity, about the first twenty segments, remain intact, and 

 the thereby injured extremities of the longitudinal vessels 

 shrink so as to prevent bleeding, it is possible to remove any or 

 all of the succeeding segments without interfering at all with 

 the circulation — a most important condition of any tenable 

 theory, and, moreover, a state of things which indicates the 

 metamerically segmented character of the vascular system, 

 always excepting the cephalisation in the anterior region." 



There appears to be entire agreement among previous ob- 

 servers as to two points only — the forward direction of the 



' Other special vessels have been described in various f^enera. In worms 

 possessing a subneural trunk there are of course branches connected with it. 

 These branches connect it, I believe, directly with the dorsal vessel, and 

 indirectly vrith the intestino-tegumentary vessels (see Jaquet, 6). Where 

 large nephridia occur the capillary network in connection with them would 

 come under the group of peripheral networks, and communicate witii branches 

 of the ventro-teguraentary vessels on tlie one hand, and with branches from 

 the subneural or (? and) intestino-tegumentary vessels on the other. 



^ I shall use the term cephalised region in the succeeding paragraphs as 

 designating that region of the body in which the vascular apparatus is not 

 similarly repeated in each segment. 



