248 Agassiz 1 Contributions to the 



the whole, we are willing to accept this view as at least oire lead- 

 ing idea to be expressed by orders in the animal kingdom. 



4. Families are characterised by general external form ; and 

 here we see no reason to differ from our author. The family is 

 in short one of the most obvious and easily recognised relation- 

 ships among animals, is almost iastinctively perceived by us, and 

 on this very account should have much more attention given to 

 it in systematic Zoology than it has yet received, as one of the 

 mo6t useful aids in the determination of species. 



"Unless, then, form be too vague an element to characterise any 

 kind of natural groups in the animal kingdom, it must constitute 

 a prominent feature of families. I have already remarked, that 

 orders and families are the groups upon which zoologists are 

 least agreed, and to the study and characterising of which they 

 have paid least attention. Does this not arise simply from the 

 fact, that, on the one hand, the difference between ordinal and 

 class characters has not been understood, and only assumed to be 

 a difference of degree ; and, on the other hand, that the import- 

 ance of the form, as the prominent character of families, has been 

 entirely overlooked ? For, though so few natural families of 

 animals are well characterised, or characterised at all, we cannot 

 open a modern treatise upon any class of animals without finding 

 the genera more or less naturally grouped together, under the 

 heading of a generic name with a termination in idee oxince indi- 

 cating family and sub-family distinctions; and most of these- 

 groups, however unequal in absolute value, are really natural 

 . groups, though far from designating always natural families, 

 being as often orders or suh-orders, as families or sub-families., 

 Yet they indicate the facility there is, almost without study, to 

 point out the intermediate natural groups between the classes and 

 the genera. This arises, in my opinion, from the fact, that family 

 resemblance in the animal kingdom is most strikingly expressed 

 in the general form, and that form is an element which falls most 

 easily under our perception, even when the observation is made 

 superficially. But, at the same time, form is most difficult to 

 describe accurately, and hence the imperfection of most of our 

 family characteristics, and the constant substitution for such 

 characters of features which are not essential to the family. To 

 prove the correctness of this view, I would only appeal to the 

 experience of every naturalist. When we see new animals, does 

 not the first glance, that is r the first impression made upon us by 



