362 C. O. WHITMAN. 
then with the first pair of eyes, we find the fourth and fifth on 
the fifth and eighth rings respectively. Now this simple 
arrangement of the eyes which is only slightly modified in 
Hemadipsa, holds good not only for Hirudo, but for 
Hemopis, Aulostoma, Macrobdella, and all the more 
closely related genera. From the fifth pair of eyes onward, 
the counting is rendered more easy by the size of the rings, as 
well as by the metameric arrangement of the colour-markings 
and the segmental papille. It is certainly very desirable that 
the various species of the above-named genera should be 
described on a common plan. It seems to me that for simpli- 
city and clearness there is no better method than the one here 
recommended. It is quite certain that no clearly marked ring 
exists anterior to the first pair of eyes that would serve the 
purpose we have in view. There are here, to be sure, in some 
species, obscure traces of what, in the opinion of some authors, 
might be regarded as one or two rings. While it is important 
to take note of all such evidences of rings, it is certainly 
advisable, for the sake of uniformity, to discard them in 
counting. 
Abbreviated Somites.—The comparison of Hemadipsa 
with Hirudo nipponia has shown that we cannot afford 
either to ignore the rings composing the two ends of the body, 
nor to pass them over with such imperfect descriptions as are 
usually accorded tothem. That the terminal somites are more 
or less abbreviated or shortened, by suppression of rings, is a 
fact recognised by all recent writers; but no one has hitherto 
thought it necessary to give more than a very superficial 
account of them. Gratiolet’s method of counting was adopted 
with a view to avoiding a close study of these somites ; and, 
certainly, it is admirably adapted to this end. Fortunately, 
the position of the five pairs of eyes has been sufficiently 
well-defined to enable us to understand the composition 
of the first four somites in Hirudo and cognate genera; 
beyond this, our information is too meagre and indirect to 
settle either the number or the composition of the abbreviated 
somites. 
