Natural History of the United States. 249 



their form, give us at once a very correct idea of their nearest 

 rela'ionship? We perceive, before examining any structural 

 character, whether a Beetle is a Carabicine, a Longicorn,' an 

 Elaterid, a Curculionid, a Chrysomeline ; whether a Moth is- a 

 Noctuelite, a Geometric!, a Pyralid, etc. ; whether a bird is a 

 Dove, a Swallow, a Humming-bird, a Woodpecker, a Snipe, a 

 Heron, etc., etc. But before we can ascertain its genus, we have 

 to study the structure of. some characteristic parts ; before we 

 can combine families into natural groups, we have to make a 

 thorough investigation of the'r whole structure, and compare it 

 with that of other families. So form is characteristic of families ; 

 and I can add, from a careful investigation of the subject for 

 several years past, during which I have reviewed the whole ani- 

 mal kingdom with reference to this and other topics connected 

 with classification, that form is the essential characteristic of 

 families, I do not mean the mere outline, but form as determin- 

 ed by structure ; that is to say, that families cannot be well de- 

 fined, nor circumscribed within their natural limits, without a 

 thorough investigation of all those features of the internal struc- 

 ture which combine to determine the form." 



5. Genera, also, are well and ably characterised : 

 "I have stated before, that in order to ascertain upon what 

 the different groups adopted in our systems are founded, I con- 

 sulted the works of such writers as are celebrated in the annals of 

 science for having characterised with particular felicity any one 

 kind of these groups, and I have mentioned Latreille as promin- 

 ent among zoologists for the precision with which he has defined 

 the genera of Crustacea and Insects, upon which he has written 

 the most extensive work extant. An anecdote which I have 

 often heard repeated by entomologists who knew Latreille well, is 

 very characteristic as to the meaning he connected with the idea 

 of genera. At the time he was preparing the work just mention- 

 ed, he lost no opportunity of obtaining specimens, the better to 

 ascertain from nature the generic peculiaiities of these animals* 

 and he used to apply to the entomologists for contributions to his 

 collection. It was not show specimens he cared to obtain, any 

 would do, for he used to say he wanted them only " to examine 

 their parts." Have we not here a hint, from a master, to teach 

 us what genera are and how they should be characterised ? Is it 

 not the special structure of some part or other, which character- 

 ises genera ? Is it not the finish of the organization of the body, 



