522 Illinois State Laboratory of Natural History. 



depression bounded anteriorly by a slight forward displace- 

 ment of the transverse ridge. The anterior pores are exactly 

 in line with or very slightly mesiad of the ventro-lateral 

 sensillse, while the posterior lie well inside of this line. 



Annuli and Somites (PI. XLVI., Fig. 33, 34).— Somite I 

 can seldom be distinguished as a distinct ring, but in well- 

 preserved preparations a pair of dorso-median sensilla' may 

 always be found anterior to and a little mesiad of the first 

 pair of eyes. Sometimes the furrow may be discerned at and 

 near the middle line, but it is always very faint and incom- 

 plete. This region bears numerous labial sense organs, 

 which are arranged in about eight transverse rows ; but, 

 except in one case in which two were found, only the one 

 pair of segmental sensilhe can be distinguished. 



Somite II consists of a single narrow annulus imperfectly 

 distinguished from the preceding and succeeding annuli. 

 The posterior furrow sometimes extends quite-to the lateral; 

 margins of the lips, but is usually very faint and imperfect. 

 This somite bears the first pair of eyes, together with dorso- ( 

 median, dorso-lateral, and dorso-marginal sensilla?, the latter 

 being very difficult to distinguish from the labial sense 

 organs. 



III is also uniannulate but is more distinct, though here 

 again the furrows are frequently incomplete. The dorso- 

 median sensilla3 are small but distinct, while the lateral and 

 marginal pairs are quite evident. A few goblet -shaped sense 

 organs form a broken transverse series. 



IV is biannulate, the two annuli uniting at the margins to 

 form the lateral boundaries of the mouth. The anterior 

 annulus is somewhat the wider and bears the eyes and the 

 full set of sensilla? toward its posterior part. It is conse- 

 quently regarded as potentially constituted of the two primary 

 annuli a 1 and al. Each annulus bears one row of goblet- 

 shaped organs. 



Y is a more fully elaborated biannulate somite. The 

 anterior annulus is decidedly the larger, and exhibits on the 

 dorsal side two transverse series of goblet-shaped organs 

 which are ventrally united into one. A full set of metameric 



