184 
TWO PRINCIPAL WORKS OF ROBINEAU-DESYOIDY 
Academy, a work almost entirely finished (‘ redige presque enticement ’), 
and accompanied by five synopses (‘tableaux’) of all the species 
Diptera of the family Muscidae observed and collected by him within 
the small area of the Departement of the Yonne. 
“ The total number of species is about eighteen hundred, of which four¬ 
teen hundred are new, or newly defined : seventeen or eighteen exotic 
genera are added. 
“ Your Commissioners have attentively examined the work of Mr. Rob.- 
Desvoidy, without, however, having been able to extend their examination 
to all the genera, and a fortiori to all the species, which, being desiccated, 
and for the most part very small, could not be analyzed. 
“ The number of new species has appeared to them in reality very con¬ 
siderable. It is possible, however, that Mr. Rob.-Desvoidy, not having yet 
formed a sufficiently positive notion of the concept of a species, which is 
fully established only when it is well characterized by appreciable differ¬ 
ences in the genital organs, has considered as distinct species mere casual 
varieties in size, villosity, and intensity of coloring. 
“Anyhow, in taking account of all these species, and in distributing 
them according to different points of view, Mr. Rob.-Desvoidy has been 
necessarily led to group them around the principal species, and that 
brought about the establishment of families and tribes that appear to 
us to a certain extent natural, although sometimes not quite distinctly 
characterized. 
“ Distinctive characters, derived from the basal joints of the antennae, 
from the joints of the arista, from the glabrousness or villosity of the un¬ 
jointed portion of the latter, have been used for the introduction of genera 
which appear to us too numerous, the more so as they seem but in rare 
cases to be supported by characters derived from tire wings and from the 
structure of the proboscis, organs that, unfortunately, have been somewhat 
neglected in the work of Mr. Rob.-Desvoidy. In examining, for instance, 
a certain number of genera which constitute the first family, the Calyp- 
trata, we have become convinced that they are merely based upon but 
very minute differences in the proportion between the second and the third 
joints of the antennae. In some cases even the genus does not show the 
character belonging to the tribe. 
“ It was undoubtedly a happy thought to introduce a connection between 
the characters of the classification of insects and their mode of life and 
habits, and thus to form families founded upon the food in the larval 
state, as well as in that of the imago. But with this method there is 
a danger of going too far, and of adopting genera and species the only dis¬ 
tinction of which would depend upon the plants, or upon the medium in 
which they live, and not upon their organization. 
