THE LEECHES OF JAPAN. 565 
thus holds a similar position in the llth somite, 
between the 38th and the 36th ring. 
The anus lies in the 102nd ring, or between this 
and the preceding one. 
The other characters of this genus, such as the maxillz, 
denticles, alimentary tract, reproductive organs, nephridia, 
&c., are too well known to require repetition here. 
I shall presently bring abundant evidence to show that the 
above characters are typical of Hirudo; and that any well- 
marked departure from this type, in the total number 
of somites, in the number or composition of the abbreviated 
somites, with perhaps the exception of the 26th somite, in 
the number or position of the eyes, nephridial pores, sexual 
orifices, &c., cannot be consistently admitted for any species 
included in this genus. If this conclusion be correct, some 
names will certainly have to be expunged from our lists of 
genera; but no objection on this ground can outweigh the 
advantages of a clearly defined and convenient standard of 
comparison. When we remember that naturalists began by 
referring almost every Leech, even Clepsine, to the genus 
Hirudo; and that some of our more recent authorities have 
gone to the other extreme, of setting up new genera on dis- 
tinctions of doubtful significance, it becomes evident that a 
genus should stand for something more than a name coupled 
with a few observations that leave us in the lurch whenever we 
seek to know its precise limits and relations to other genera. 
A close comparison of the Japanese Medicinal Leech with 
those imported from Sweden, and with those which I collected 
myself in Saigon, Singapore, Ceylon, and Naples (Sebeto 
River), enables me to say that all the characters above named 
are common to these widely separated and distinctly marked 
species. It is more than probable, therefore, that Gratiolet 
was in error as to the number of rings in the 7th and 8th 
somites. 
Aulostoma and Hemopis.—I have been surprised to 
find such a close agreement among the different species of 
Hirudo, in regard to the number and character of the rings as 
VOL. XXVI, PART 3.—NEW SER, BB 
