The Hirudinca of Illinois. 513 



surface of the upper lip deeply into two halves, hut fades out 

 posteriorly ; at least one fainter sulcus appears on each side. 

 Somites I-IV constitute the lip and sucker, and the united 

 annuli of V form the postoral annulus. 



The five pairs of eyes (PL XLIV., Fig. 12, 19) present 

 the arrangement usual in the family, except that the second 

 and third pairs are closely approximated, owing to the posi- 

 tion of the latter very close to the anterior border of somite 

 IV. The fourth pair also is somewhat in advance of the line 

 of sensillge. 



No specimens have been seen in 'which the clitellum is 

 sufficiently developed to permit of the determination of its 

 form and extent. 



As Verrill ('74) long ago pointed out, the external genital 

 region (PI. XLIV., Fig. 16) is very remarkable; in some 

 respects, indeed, unique among known leeches. This is true 

 not only of the elaborate adhesive arrangements, which are 

 probably important aids to successful copulation, but also of 

 the location of the genital apertures. The features of this 

 region have been described by Moore ('98) from examples 

 collected in Louisiana, but are now figured for the first time. 

 The figure is a composite of the three specimens which this 

 collection contains and which differ from one another in cer- 

 tain particulars. 



Comparison of the previous account with this figure will 

 bring to notice some disparity in minor details, due to the 

 fact that almost every specimen presents some individual 

 peculiarities. It is very probable that this results not more 

 from individual variability than from the temporary, seasonal, 

 and developmental character of the structures concerned. 



In specimens sexually inactive the male pore appears 

 near the anterior margin of XII a 2 ; the female pore, on XIII 

 b 1. They are surrounded by a more or less wrinkled area in 

 which appear a variable number of copulatory gland pores 

 more or less conspicuously developed. Omitting consider- 

 ation of intermediate states the active condition is represented 

 in PI. XLIV., Fig. 16. The surface immediately surround- 

 ing and succeeding the male pore is inflected as a deep pit 



