60 



I'fgard to the order of development of annuli towards the consti- 

 tution of a triannulate somite, namely, that the annuli are 

 developed alternately posteriorly and anteriorl)' to the sensory 

 annulus. The anterior extremit}'^, or " head," although not 

 forming a distinct " capula " as in other Ichthj'obdellids, 

 represents a number of fused annuli or somites whose lines of 

 ■division are not shown externally on the lijody-surface, beyond 

 that the margin of the " head " is furrowed as far as the midline. 



Semilageneta HUH. — In my original description of this genus I 

 pointed out that the somite was triannulate, and that the limits 

 of the somites were denoted in the anterior part of the body by 

 the presence of distinct papilhe, and in the remaining body- 

 portion by the outline of the body which was divided into 

 segmental regions, consisting of three annuli, by well marked 

 sulci. These areas I still consider to represent distinct somitic 

 divisions. Passing forwards from xii., which is the first of the 

 somites thus marked off, we find xi. triannulate and carrying 

 papillae on the first and not on the second or middle annulus- 

 This distribution of the papillae then agrees with Whititian's plan' 

 and not with that of Castle. 



Addendum to original description. — I originally placed Semi- 

 lageneta among the Glossiphoniidiv, but, judging from the po.sition 

 of the genital aperture, it should find its place among the Ichthy- 

 obdeUida:'. The nature of the anterior extremity, however, is 

 distinctly intermediate between that found in the IcJithyohdellidm 

 and G/ossiphoniidce, there being no capula developed as in the 

 former of these two groups. 



PJiiloimoit pungens. — In examining some killed specimens of 

 this species, n)y attention was attracted to a regular separation of 

 groups of annuli on the ventral surface, and, strangely enough, 

 these groups consisted of four annuli. The leech is readily seen 

 to be tetrannulate from the distribution of the jiapilhie. The 

 fuirows or gaps which occurred on the ventral surface, dividing 

 off groups of foui' annuli, seem, then, to mark off the somite- 

 limits, inasmuch as the number of annuli composing the groups 



