8 
The Genera and Species of Mallophaga 
preferred to tear them from their natural surroundings and transfer 
them to an utterly unrelated group, simply because the existing generic 
definition seemed to him the better to include them. The second case 
is that of his Degeeriella charcoti, which is a petrel Lipeurus closely akin 
to L. gurlti. Here, again, he has chosen, rather than expand the 
definition of the genus Lipeurus, to transfer the species from its natural 
position. The sequel has been that Mjoberg, comparing the species 
with those among which Neumann had placed it, has erected for it a 
new genus Pseudonirmus (Nirmus = Degeeriella), which I discard at 
present, but which will ultimately have to be used for that group of 
petrel Lipeuri ranging from L. gurlti to L. charcoti, a group which has 
nothing whatever to do with Nirmus. It is cases such as these which 
induce me to ask for accurate determination of affinities. We do, after 
all, propose to deal with organisms, not definitions. 
If these affinities can be indicated, the species to be described is at 
once limited to a more or less small group, with many features in common, 
such features serving no good purpose in a specific description. We 
now want actual diagnostic characters, and the question is—Where may 
these best be found ? I have no desire at present to lay down any 
scheme of description, but I myself find the best characters for separating 
closely related species in the following points: The general proportions 
of head and thorax; the structure of that part of the head in front of 
the mandibles, dealt with in a cleared mount, not simply on the dorsal 
surface; the thoracic sternites; the genital plate and blotches of the 
9; and the chitinous genitalia of the (J. In the Amblycera, a careful 
study of the lateral region of the head, both dorsally and ventrally, is 
important. In many species outstanding features occur in other parts; 
but, with careful figures, a description of the parts I have mentioned 
should suffice. 
Waterston has already insisted on the value of the S genitalia, 
which certainly present the very best characters obtainable. Nor are 
these difficult to prepare for examination. If the insect be heated in 
10 per cent, caustic until the soft parts are destroyed, then passed into 
glacial acetic acid, and from that into oil of cloves, a few touches with 
fine needles under a binocular microscope will serve to separate the 
genitalia from the body, and both may be mounted directly into balsam 
on the same slide. After very little practice, the dissection of the 
genitalia hardly involves any addition to the time occupied in making 
mounts. 
With regard to figures, I think it is desirable to have a complete 
figure of each insect, supplemented by more highly magnified figures of 
