334 C. O. WHITMAN. 
from the central position required for maintaining the equili- 
brium in swimming to a point nearer the posterior sucker, 
keeping pace with the gradual concentration of muscular 
power in the sucker and posterior end of the body. The body 
became more cylindrical, the acetabulum and the posterior 
extremity stouter, thus enabling the Leech to poise on this end 
with great ease when reaching about for its victim. 
The Segmental Papille.—In the foregoing comparison 
of the rings and somites of the land and the aquatic Leeches, 
attention was called to the position of the eyes and the seg- 
mental papille; and this leads us to a point of considerable 
importance, namely, the significance of the papille. 
In the Land Leech, the epidermis is broken up into quadran- 
gular and polygonal areas ; and the larger areas are the seats 
of the eyes and the papille. The number and arrangement of 
these areas on the cephalic lobe are very regular and uniform 
in different individuals of the species. Behind the head the 
areas are arranged in transverse rows corresponding in dia- 
meter to the thickness of the rings. This division into areas 
extends to every part of the Leech, and gives the surface that 
rough appearance which Grube has described as “ granular.” 
In addition to the segmental papille, which, from their size 
and metameric arrangement, are very conspicuous (figs. 6 and 
7), there are numerous smaller papille which amount to only 
slight rounded elevations situated at the centre of the areas 
which are not occupied by the eyes or the segmental papille. 
In the posterior region of the body the segmental papille are 
conical in form, with rounded summits which are pale yel- 
lowish white and translucent. At the centre of the summit 
there may be seen a minute dot of a plumbeous hue, which 
has the appearance of a pore. Sections show that there is no 
pore, and that the dot is merely a minute unpigmented portion 
of the solid papilla. Towards the head the papille become 
more and more flattened; but their lighter colour and the 
larger size of the lead-coloured central dots make them quite 
distinct. Owing to the bilaterally symmetrical arrangement 
of these papillz on the first ring of each somite, there are as 
