MOORE: HIRUDINEA OF SOUTHERN PATAGONIA. 671 



between the third and fourth pairs of eyes is somewhat greater than that 

 separating any of the preceding pairs, no distinct intervening annulus 

 can be detected. 



V is biannulate; the two annuli (ai + a2) and aj are of about 

 equal length. The pigment cups of the fourth pair of eyes are at about 

 the middle of the anterior annulus and placed on the antero-internal face 

 of the sensory cells. The furrow (ai-\-a2)/aj is incomplete in the small 

 specimen and the pigment cups of the eyes reach into IV, an appearance 

 due in part to contraction and in part to the position of the head when 

 drawn. 



VI is also biannulate. On the dorsal surface a faint furrow (aila2] is 

 present, extending about as far as the eyes in the larger example, but 

 detectable under the compound microscope for the entire width of the 

 head of the smaller one. The pigment cups of the fifth pair of eyes, 

 which cover the anterior face of the sensory cells, lie directly beneath this 

 incipient furrow. The second annulus (aj) is quite distinct all around, 

 making the somite biannulate ventrally as well as dorsally. 



VII is triannulate ; aj is distinctly longer than ai or a2 which are 

 obviously more closely associated, the furrow ail 0,2 being less distinct 

 than a2/aj, especially on the ventral surface. 



VIII is quadriannulate. Of the four annuli ai is just appreciably longer 

 than a2 and shows a faint dorsal furrow, bilb2 ; b$ and bd are distinctly 

 shorter than ai and a2, and the furrow b$lb6 is a trifle less deep than 

 the others. 



There are sixteen distinctly quinqueannulate somites, IX to XXIV in- 

 clusive. In IX the relative lengths of the annuli are represented by the 

 formula bi = b2 < b$ = b6 < a2 ; IX bi and b2 = VIII b$ and 56. By 

 about XI the formula becomes bi=b2 b^ b6<a2, which it remains until 

 about XXII where the somites begin to decrease in relative and abso- 

 lute length, owing to diminution of the posterior annuli. Here 

 a2 > bi = b2 > b$ b6. 



XXV is quadriannulate, bi and b2 being smaller than a2, which is 

 again slightly smaller than aj. Across the latter, traces of the furrow 

 b$lbd may be detected. Following XXV are two small rings between 

 which the anus is placed. Although there are no visible sensillae to 

 authenticate the determination, these are interpreted as XXVI and XXVII 

 respectively. 



