328 Agassiz’s Contributions to the 
very characteristic as to the meaning he -connected with the idea of 
genera. At the time he was preparing the work just mentioned, he lost 
no opportunity of obtaining specimens, the better to ascertain from nature 
the generic peculiarities of these animals, and he used to apply to the 
entomologists for contributions to his collection. It was not show speci- 
mens h to obtain, any would do, for he used to say he wanted 
them only ‘to examine their parts. Have we not here a hint, froma 
master, to teach us what genera are and how they should be character- 
ized? Is it not the special structure of some part or other, which char- 
acterizes genera? Is it not the finish of the organization of the body, as 
worked out in the ultimate details of structure, which distinguishes one 
genus from another? Latreille, in expressing the want he felt with refer- 
orm. Nor are genera merely a more comprehensive mould than the 
or at least a petitio principii, not admissible in a_philosop saat | 
peci 
as the other, 
& petitio principti. The subject is one for investigation, an¢ - 
which direct study of the actual intercourse of admitted ee 
Species is but barely begun; science is far from a pee 0 a 
; enti 
Journal 
. . i i i i h 
times too indefinite to allow of the safe use of this criterion ae 
regard to species. We should claim that feat is a Pe raele 
inci ; Fe oe *ou istinct to oe 
igated; that the limit is so obviously : tial to the © 
