30 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxi. 



tation, wlien it is of a persistent type, is as much an anatomical fact as 

 tbe development of other dermal outgrowths like spines or claws. The 

 combination, then, which makes tlie species of this genus recognizable 

 consists of the somewhat retracted head, rather short untufted thorax, 

 rather long untufted abdomen, unarmed legs, simi)le antennae in both 

 sexes, and white or gray primaries, in which there is usually a black 

 basal dash and a streak opposite the anal angle, which may or may not 

 cross the transverse posterior line. 



It has been the habit to refer to this genus as one in which the adults 

 are remarkably similar and offer no strong characters, while the larvae 

 and even pupae afforded obvious and definite features for systematic 

 purposes. These statements are made without knowledge of the 

 structure of the insects and the amount of variation that actually occurs. 



Mr. A. K. Orote, to whom we are indebted for the descriptions of 

 several of our species of Acronycta, has also given us a number of lists 

 and classifications in which generic and subgeneric names are api)lied 

 to the groups and other divisions. These divisions are in the main 

 based upon superficial appearance and resemblance and not upon 

 structure or other characters of real systematic value. They were 

 therefore incai)able of accurate definition, and with one exception none 

 of the proposed names can be used. In 189G he published Die Apa 

 teliden as No. 3 of the Mittheilungen aus dem Koemer Museum in 

 Hildesheim, and this is based upon larval characters supplied by Dr. 

 Dyar and upon the published work of Dr. Chapman. No addition is 

 made to our knowledge of adult structure and only the order in which 

 the species are arranged is original. 



As a matter of fact, the species of Acronycta afford excellent charac 

 ters for groupings in the adult stage, and this is only what we should 

 expect. It is unquestionably true that there may be independent vari- 

 ation in the larval stage, necessitated by the environment, but it is 

 equally true that there can be no variation in any important structural 

 or anatomical derail which will not also be marked in the adult. I am 

 not so certain that the opposite is true, however, and am inclined to 

 believe that structural differences in the adult may exist without obvi- 

 ous effect on the early stages. I am not inclined to fully agree with 

 Dr. Scudder that genera are as easily traced in the larva as in the 

 imago, and rather believe that, while adaptive or protective variation 

 may occur in the early stages without effect upon the adult, all anatom- 

 ical differences originate in the adult. Variation in the adults is also 

 determined very largely by environment, and this is particularly true 

 of adaptive variation. It is quite conceivable that real changes of 

 structure may have taken place which are not in the least indicated by 

 the superficial appearance. This, indeed, has happened in Acronycta. 

 The species as a rule rest during the day openly upon the trunks and 

 branches of trees, or upon stones, and their colors and markings are 

 well adapted to harmonize with such surroundings and to render the 

 resting specimen invisible. So long as this iniaginal habit persists 

 there is not much likelihood of any change in the general character 



