380 A. SEDGWICK. 
acters, there is not the slightest difficulty in assigning all of the 
known species to their groups. When, in 1888, I recognised 
the existence of this grouping, I carefully considered the 
desirability of establishing them as distinct genera or sub- 
genera, but I came to the conclusion that it would be rash to 
do so, partly because it was by no means certain that they 
would stand the test of later discoveries, and partly because 
the known species were so small in number and so easy to 
handle from a classificatory point of view, that there did not 
appear to be any advantage to be gained by so doing. 
It is now twenty years since the publication of my mono- 
eraph, and it is of interest to inquire to what extent later 
discoveries have confirmed or disproved the conclusions I 
then came to. The present is a particularly appropriate time 
for doing this, on account of the recent publication of 
Professor Bouvier’s fine monograph on the genus. In this 
important work M. Bouvier has accurately recorded the 
characters of a considerable number of new species; he has 
defined with precision some species of which very little, some- 
times nothing, was known; he has added greatly to our 
knowledge of the anatomy of the genus; and lastly, he has 
established the existence of two new primary localities for 
the group. By primary localities I mean localities in which 
all the species possess a set of characters which differentiate 
them from any of the groups of species previously recognised. | 
These are the Congo and Chili. It is true that Bouvier 
associates these two newly defined species with certain of the 
older groups; he associates the Congo Peripatus with the 
Neotropical group, and the Chilian species with a section of 
the South African, but I do not agree with him in this, and 
it is the object of this paper to inquire (1) whether he is justi- 
fied in making this association, and (2) whether the creation 
of genera and the association of them into families and sub- 
families is in the interest of zoological science at the present 
time. Before doing this I may briefly recall the other 
important systematic work which has been done on the genus 
since 1888. In 1898 Willey described a new species which 
