28 BRISTOL. [Vol. XV. 



Head Region. 



The innervation of the rings of the head region shows, as 

 will be demonstrated later, the limits of the reduced somites 

 to be as follows : (Fig. 3) I consists of the prostomium ; II of 

 rings No. 2 and 3 ; III of a single broad ring, No. 4 ; IV of a 

 single ring, No. 5 (this ring lies in the plane of fle.xion of the 

 body on the oral sucker and is very narrow) ; V consists of 

 three rings, Nos. 6, 7, and 8 ; VI consists also of three rings, 

 Nos. 9, 10, and 1 1. 



Anal Region. 



In the anal region (PI. VI, Figs. 3 and 7) the innervation shows 

 the limits as follows : XXV consists of rings 102, 103, and the 

 anterior half of 104. XXVI consists of the posterior half of 

 104 and 105. 105 is a broad ring which in some individuals 

 shows a tendency to divide into two, sometimes three, rings. 

 It lies in the plane of flexion between the body and the anal 

 sucker. XXVII consists of 106, the last ring of the body and 

 the dorsal area of the sucker. XXVIII to XXXIV consist of 

 the sucker disc. External evidence of this is found in the six 

 radial lines of sensillae on either side of the median plane. 



Stimniary. 



The number of rings is 106 from prostomium to sucker. 

 The first pair of eyes (Fig. 4) lies in the 2d ring ; the second 

 pair lies wholly in the 4th, while the third pair lies usually 

 between the 4th and 5th rings. The clitellum consists of 

 fifteen rings, Nos. 28 to 42 inclusive, or the 2d to sth ring 

 of somite X, the ten rings of XI and XII, and the ist ring of 

 somite XIII. The male orifice lies, usually, between the 36th 

 and 37th rings. The female orifice between the 38th and 39th 

 rings. 



The anus opens in the hinder portion of the 104th ring, or 

 between the 104th and lOSth rings. 



The first nephridiopore lies between the i6th and 17th 

 rings ; the last and 17th nephridiopore lies between the 96th 

 and 97th rings. 



