288 C. O. WHITxMAN. 



wards later), and then bend forward along the margin of the 

 body, and enter the ventral trunk near the fore end of the body. 

 The next pair pass outward over tlie first pair of diverticula to 

 the margin of the body, and then forward, entering the ventral 

 trunk just a little in advance of the posterior pair. The next 

 pair leave the dorsal trunk asymetrically, the left taking its de- 

 parture at a point farther forward than the right. Both pass 

 forward to the lateral lobes or angles of the head, and then back- 

 ward, entering the ventral trunk just behind the cephalic pair. 

 The odd pharyngeal branch (;;. b) leaves the dorsal trunk just 

 behind the cerebral ganglia {c. r/), then passes forward or back- 

 ward, according to the position of the pharynx (backward in the 

 figure), to the hind end of the pharynx (^j.), then forward along 

 its median dorsal line; near the fore end it splits into two 

 branches which, diverging, encircle the pharynx and unite again 

 on its ventral surface ; the course is then backward to the base 

 of the pharynx ; from this point it passes forward again, and 

 finally enters the ventral trunk between the cephalic branches 

 (c. b.), thus forming the anterior end of this trunk. The ventral 

 trunk lies just above and in close apposition to the ganglionic 

 chain. When the pharynx is protruded it passes through the 

 oesophageal nerve-ring, and with it the ])haryngeal branch (;j h) ; 

 the main ventral trunk {v. t.) remains in the position given in the 

 figure. The dorsal trunk {d. /.) splits into two branches ])os- 

 teriorly, which unite again just behind the anus, thus producing 

 an anal ring. Into this anal ring seven pairs of branches enter, 

 which come from the posterior end of the ventral trunk. All 

 the branches above given I have traced many times with great 

 care, and I believe they represent all the connections between 

 the dorsal and ventral trunk. Ley dig and Bidder found only 

 two of the four pairs of anterior branches which I have described. 

 Leydig supposed that they terminated in the posterior disc, but 

 Bidder was undecided about it. In the dorsal trunk are found, 

 as Bidder has already stated, several " valves.'^ These consist 

 of cell clusters, which have but one point of attachment to the 

 wall of the vessel. During the diastole the valves are thrown 

 forward and to one side, and during the systole they lie trans- 

 versely, closing the lumen of the vessel. The nearly colourless 

 fluid of the system just described contains a few corpuscles, 

 which are easily seen when the blood is made to flow slowly by 

 pressure. 



The marginal sinus, usually spoken of as two lateral sinuses, 

 is a continuous channel, passing entirely around the animal and 

 returning into itself. The median sinus, in which the ganglionic 

 chain and ventral trunk apj)ear to lie, can be traced through the 

 entire length of the body ])ro])cr. '^^Phe transverse chnnnels, 

 joining the median with the marginal sinus, often anastomose 



