The Hirudinea of Illinois. 515 



Besides those mentioned, two or three additional pairs are 

 located far from the middle line on annuli XIII bl, a 2, 

 and b5. 



Each of these pores is the crescentic or slit-like external 

 orifice of a little subcutaneous bursa, usually filled with a 

 more or less hardened substance which may raise the integu- 

 ments into a small papilla and is probably the secretion of a 

 mass of glands (eg I) occupying the whole of the middle region 

 of somites XII and XIII and covering the walls of the male 

 pit internally. 



Seventeen pairs of nephridiopores (PI. XLIV., Fig. 13, 14) 

 are situated on small papillae near the posterior margins of 

 annuli VII ((1 to XXIV b'2 inclusive. The posterior are 

 entad, the anterior ectad, of the ventro-lateral sensillse. 



Annuli and Somites (PI. XLIV, Fig. 12-15, 18, 19).— Ex- 

 cept in a few minor respects the incomplete somites possess 

 the same number of rings as in Macrobdella and Hcemopis 

 marmoratis. 



Fifteen somites (IX to XXIII inclusive) are complete and 

 quinqueannulate, b l-\-b 2+a % + b 5 + /? 6. In each of these, 

 except IX, a '2 is just perceptibly shorter than the others and 

 is less likely than they to show the depressed transverse 

 line, though the raised line just behind the sensillre is quite 

 as distinct. 



The sensillae are very regular in arrangement but very 

 small. They appear as white circular spots, and, in the best 

 preserved examples, are distinctly but very slightly elevated, 

 above the surface. They encircle the exact middle of the 

 annulus. The dorso-medians (md) are very close together, 

 scarcely an annulus length apart. About twice this distance 

 separates these from the dorso-laterals (dl) ; from the 

 dorso-laterals to the dorso-marginals (dm) and also from the 

 latter to the supra-marginals (sni) the distances are slightly 

 greater than that first mentioned. Owing to the flatness of 

 the ventral surface the relative positions of the sensillre as 

 shown in Figures 13 and 14 represent accurately the 

 distances which separate them. 



There are eight incomplete somites at the anterior end. 



