THE LEECHES OF JAPAN, 369 
that we must find some better basis for distinguishing genera 
than has yet been offered in the case of Hzmopis. 
The Somites as a basis of Classification. 
I shall conclude my remarks on the somites as a basis for 
distinguishing genera, by a comparison of genera from different 
countries. That such an important basis of classification has 
thus far been completely ignored, is due to the fact that the 
segmental papille have hitherto attracted very little attention. 
It is the metameric arrangement of these peculiar sense- 
organs, which I regard as incipient eyes, which has revealed to 
me the degree of abbreviation that has taken place in the 
terminal somites, and thus led to the discovery of characters 
which serve to fix precise limits to genera, and to determine 
their phylogenetic relationship. The following descriptions, 
added to those already given of Hemadipsa and Hirudo 
nipponia, will make clear the facts on which some of the 
foregoing conclusions rest. 
1. Hirudo medicinalis (Sweden). In order to define 
the position of the segmental papille, the colour markings 
must be briefly noticed. In the specimen examined the dorsal 
surface was marked by six brownish-yellow stripes. The two 
median stripes were about one third of the width of the body 
distant from each other, and thus divided the dorsal surface 
into a median and two lateral areas. The lateral stripe of each 
side lay near the median stripe, separated from it by consi- 
derably less than half the width of the lateral area. On every 
fifth ring (last of each somite) the lateral stripe inclosed a more 
or less triangular black spot, the more elongated angle of 
which pointed forward. Similar spots, but much smaller, were 
also seen in the median stripes on the same rings. The two 
latero-marginal stripes were very narrow and were separated 
from the yellow margins by a narrow black stripe. This black 
stripe widened on the last ring of each somite, in the direction 
of the middle dorsal line, thus causing the latero-marginal 
stripe to form a curve at these points in the same direction. 
The median and lateral stripes coalesced on each side near the 
