516 Illinois State Laboratory of Natural History. 



I is incompletely separated from II and bears but one pair of 

 metameric sensillse. II is a narrow imperfectly differentiated 

 annulus bearing the first pair of eyes and, externally to these, 

 three pairs of sensilla?. Ill is also uniannulate, and the 

 second pair of eyes which it bears represents the dorso-lateral 

 sensillre, the other three pairs being unmodified. 



IV is biannulate (al + a2)+a3. The first ring is wider 

 than the second, and its composition is indicated by an inter- 

 rupted furrow which passes across the third pair of eyes but 

 anterior to the other sensillse. V differs from IV only in its 

 somewhat greater length and its relation to the mouth. 



VI and VII are each triannulate ; the latter is considerably 

 the larger, but in each the annulus a 3 is dorsally about two 

 fifths of the entire length of its somite and in VII shows a 

 slight furrow all around. The furrow VI a 1 /a 2 disappears 

 ventrally. 



VIII is quadriannulate ; a 1 is longer than a 2 and faintly 

 subdivided all around, but is not equal to VII a 3 ; b 5 and 

 b 6 are fully developed and about equal to a 2. 



In IX the relative size of the annuli isM=£2 <a1 <b5=b6 ; 

 in X, £l=£2=a2 <bo=b6 ; and in XI and succeeding somites 

 bl=b%=b5=b6> a'2. The posterior annuli of XII and the 

 anterior of XIII are somewhat contracted in length. 



in XXIII. b5 and b6 are relatively slightly shorter, while 

 in XXIV they are no longer distinct, the separating furrow 

 being very shallow, so that this is counted as a quadri- 

 annulate somite. Bl and b 2 are longer than a 2. 



XXV is a contracted quadriannulate somite in which the 

 following relative proportion exists in the lengths of the 

 annuli of the specimens examined : £l=a3>a2 — #2. 



XXVI presents the following variations : In the specimen 

 drawn it is a single large annulus, particularly long at the 

 sides, where a faint emargination and slight dorsal depres- 

 sion indicate an incipient division at about the middle. 

 The sensilla? are fully developed and lie well toward the pos- 

 terior margin of the ring. Another example from the same 

 lot has this somite very distinctly and completely divided on 

 the dorsal side into two annuli, of which the anterior is almost 



