﻿108 CLEMENS' SYNOPSIS OF 



therefore, to determine, as well as we may be able, in what a generic diagnosis of the 

 perfect individual should consist, and to point out in general terms, the organs and 

 parts in which the indications of generic differences may be looked for. It is, per- 

 haps, scarcely necessary to repeat, that these will not be found expressed to the same 

 degree, in all the organs at the same time in the various groups, and that the special 

 variations must be valued according to the agreements or differences in general struc- 

 ture. We would look for generic characters then, in the development of the head 

 and its relations to the thorax, and in the agreements of the various parts of the body 

 with each other ; in the accessory cephalic organs, the eyes, the ultimate peculiarities 

 of the antennas ; in the characteristics of the oral apparatus, the labial palpi, the ru- 

 dimental or developed condition of the internal and external maxillary palpi, and as 

 intimately connected with these and the digestive system, the development of the 

 tongue; in the peculiarities of the wings and a general similitude of ornamentation. 

 Inasmuch, however, as the latter is liable to specific variability, its value is purely 

 secondary, although a tendency to the repetition or reproduction of ornamental forms, 

 may be constantly observed in most well marked groups. It is but rarely introduced 

 into the generic diagnosis, for this should be readily recognized by those characters 

 which are indicative of physiological structure. It may afford hints as to generic 

 affinities, but should be disregarded when the more permanent portions of structure 

 are divergent, or when these are correspondent and the ornamentation but slightly 

 different. 



In connection with the generic group, it may be proper to remark, that it is well 

 known the genera of the early writers are in a great measure recognized as families 

 at the present day. They depended chiefly on the various antennal forms for the 

 establishment of these groups, and I would here call attention simply to the corres- 

 pondence between general antennal forms, and the general pterogostic structure of 

 the wings. Besides this, there is the fact, that the distinctive form of the antennae 

 belongs to the imago period ; that, their development and that of the wings are extem- 

 poraneous events, the former taking their peculiar structure only with the addition or 

 acquisition of the organs of flight. The antennae, however, frequently undergo modi- 

 fication which is not expressed in the wings, and the structure of these on the other 

 hand, vary from a typical pattern, in many instances, without the variation being 

 markedly shown in the antennal organs. In the group at present under considera- 

 tion, there is absolutely no generic modification of the pterogostic structure, in any 

 member of the entire family that has come under my observation. But, the an- 

 tennae, on the contrary, undergo changes in ultimate structure, the most aberrant 

 species in this respect being found in the genus Smerinthus. The attempt to find 

 generic characters in the separation or approximation of the branches of the median 

 vein or nervure, is essentially artificial ; for special investigation proves, that in this 



