ON THE STRUCTURE OF VERMICULUS PILOSUS. 255 



The vascular system is very peculiar. In fig. 5 the main 

 blood-vessels have been represented somewhat diagramraatically, 

 omitting for the sake of clearness the complex fine network 

 found all over the first ten segments. A large longitudinal dorsal 

 vessel (fig. 5, d. v.), reaching from the brain to the last segment, 

 gives off on either side in front of each septum from the 3nd 

 to the 10th segment a lateral dorsal vessel (fig. 5, /. d. v.), 

 which soon branches out over the body-wall, reuniting below 

 into two lateral ventral vessels which enter the longitudinal 

 ventral vessel (fig. 5, v. v.). One of the lateral ventral vessels, 

 the smaller, enters the ventral vessel about the middle of the 

 segment (fig. 5, m. I. v. v.) ; the other, and larger, runs into it 

 towards the hinder end of the segment (fig. 5, p. L v. v.). In 

 my preliminary note I stated that there were a pair of " hearts " 

 in the 10th segment ; this was a mistake. Indeed, the fact 

 that there is no direct communication between the 

 longitudinal dorsal and ventral vessels is the most 

 striking thing about the blood-system of Vermiculus. The 

 manner in which the lateral dorsal communicate with the 

 lateral ventral vessels by means of the cutaneous network is 

 shown in fig. 9. In the post-genital region only small vessels 

 are given off at each segment to the body-wall and to the 

 intestine. 



The dorsal longitudinal vessel from the third to the last 

 segment is dilated in front of the region where each pair of 

 lateral vessels is given off into a small bulb or swelling, round 

 the posterior constricted edge of which are ranged large cells 

 (often as many as eight or nine), forming a system of valves 

 (figs. 8 and 10, v.). Each cell is attached at its posterior end 

 only, while its main body can swing backwards and forwards ; 

 it contains a number of bright fatty granules and a small 

 spherical nucleus (figs. 8 and 10). The lateral dorsal vessels 

 increase in size from the 2nd to the 10th segments ; from the 

 3rd segment to the 10th they have an increasing number of 

 dilatations and constrictions, each provided with valves similar 

 to those in the longitudinal vessel (figs. 5 and 10). The 

 vessel in the 10th segment, which is by far the largest, has as 



