318 C. O. WHITMAN. 
Leeches, which form together a new genus (Leptostoma!) ; 
and a comparison of a few Asiatic, European, and American 
forms. 
A considerable portion of the paper is devoted to a com- 
parative study of the different genera, with a view to finding a 
more satisfactory basis for classification than has hitherto been 
employed. 
It has been found that all the Hirudinide agree in having 
twenty-six somites represented between the first pair of eyes 
and the acetabulum ; and a careful study of the annular com- 
position of the somites in different genera has revealed a law 
of abbreviation which holds true of both ends of the Leech. 
The extent of this abbreviation, which consists in the suppres- 
sion of from one to four of the less important rings in the 
extreme somites, furnishes one of the best means for distin- 
guishing genera and species, and at the same time gives us a 
key to their phylogenetic relationship. 
A prominent place has been given to the Land Leech, one of 
the most interesting and instructive forms, and one which has 
hitherto received very little attention. An attempt has been 
made to arrive at satisfactory views respecting its origin and 
affinities ; and some general conclusions, based on a compara- 
tive study of a considerable number of species from different 
countries, have been offered in advance of a monograph now in 
preparation, which will treat of the entire family. 
The Medicinal Leech has been compared with species ob- 
tained in Saigon, Singapore, Java, Ceylon, Naples, Sweden; 
and the genus Hirudo defined with the precision required to 
make it a convenient standard of comparison. 
Internal structure has been dealt with to a limited extent ; 
and some interesting facts, especially in relation to the nephri- 
dial organs of the Land Leech, have been obtained. 
One of the most important points made clear in the course 
of the paper is the existence of from twelve to fourteen sense- 
1 Tn a preliminary paper (‘ Proc. Amer. Acad. Arts and Sci.,’ vol. xx, Sept., 
1884) I have used the name Microstoma, not being aware at the time of 
writing that the same name was already in use, 
