366 , C. O. WHITMAN. 
well as the number and composition of the abbreviated so- 
mites; and still more so, to find these characters repeated with 
all the more important details of number and position in both 
Hemopis, and Aulostoma. This certainly indicates a close 
relationship between the three genera. Aulostoma is, how- 
ever, a well-founded genus, distinguished from Hirudo by its 
habits, mode of life, form of its alimentary canal, character of 
its teeth, and the position of the male orifice, which is in the 
middle of the 3lst ring, instead of between this and the 
30th. In the case of Hemopis, the distinctions are so few 
and unimportant that it is difficult, if not impossible, to 
justify a separation from Hirudo. Hemopis is a complete 
copy of Hirudo in all the particulars before named, and its 
highest claim to generic rank is based on the small number of 
its denticles. In view of the great variability in the number 
of the denticles, not only among different species of one and 
the same genus but also among individuals of the same 
species, and even in the different jaws of the same individual, 
this distinction hardly deserves generic rank. The other dis- 
tinctions on which this genus rests, whether considered singly 
or collectively, are even less satisfactory as generic characters. 
Leuckart! long ago declined to recognise Hemopis as a dis- 
tinct genus. After defining the genus Hirudo, he remarks :— 
‘Thus characterised, the genus Hirudo embraces not only 
the larger number of species hitherto referred to it—with the 
exception, e.g. of H. lateralis, Say—but also the genus 
Hemopis, the separation of which we must regard as unsound 
so long as the usual distinctions (‘ body less flat, less deeply 
annulated at the margin, in contraction less olive shaped, 
denticles less numerous ”) are not replaced by others of a more 
positive value.” 
Hirudo and Hemopis both require the same food, and 
obtain it from the same sources and by the same means, with 
the single difference, that Hemopis, which is provided with 
denticles too short and dull to make an incision in the epi- 
dermis, is restricted in its attacks to epithelial surfaces which 
‘ Leuckart, ‘Die menschlichen Parasiten,’ i, p. 716, 1863, 
