360 C. O. WHITMAN. 
different starting-points, are thrown out of relation, and confu- 
sion is the consequence. The confusion consists in this, that the 
dorsal and ventral halves of the same ring bear two different 
numbers. In the case of Macrobdella decora, for instance, 
the dorsal half of the buccal ring, according to Verrill, is counted 
as the 6th, five rings preceding it; while the ventral half is called 
the Ist, starting from the mouth. In the same way the male ori- 
fice is said to lie in the 27th ring behind the mouth: but what is 
the number of this ring on the dorsal side ? It is certainly a very 
simple matter to add five, the number of rings supposed to 
belong to the cephalic lobe, to twenty-seven; but this alone 
would not give us the number on the dorsal side in any Leech 
which, like the Medicinal Leeches of Europe, China, and Japan, 
has four rings (two buccals and two post-buccals) represented 
by two on the ventral side. The simplest method, and the one 
least liable to confusion, seems therefore to be that of num- 
bering the rings from one fixed point on the dorsal side. Each 
ring then has a definite number and precise relations. 
Gratiolet was the first to emphasize the importance of a well- 
defined starting-point in counting, as a means of determining 
with precision the position of the genital pores. Under the 
persuasion that no such point could be found on the dorsal side 
which would be convenient in use, he recommended the pos- 
terior pair of nephridial pores as the most satisfactory point of 
departure, reckoning from this point forward. The considera- 
tions which led him to adopt this unconventional and somewhat 
awkward method, may be seen from the following: 
“La chose importante dans cette recherche serait de partir 
d’un point fixe et nettement défini. Or, la plus grande incer- 
titude régnant sur le nombre des anneaux aux deux extrémités 
de l’animal, il faudrait en conséquence pouvoir les négliger. 
En y réfléchissant un peu, le probléme ne paraitra pas absolu- 
ment insoluble. Quand on étale une Sangsue morte ou 
vivante, et qu’on la fait glisser sur sa face dorsale appliquée 
sur la convexité du doigt indicateur, on apercoit, d’espace 
en espace, deux petites gouttelettes de liquide symétriquement 
accumulées sur le bord postérieur de certaines anneaux. Ces 
