NATURAL SCIENCES OF PHILADELPHIA. 25 



particular species make their appearance in the same locality. A 

 combination of circumstances exists to impose an effectual check 

 upon the undue multiplication of insect life, where nature is not 

 interfered with b}>- man's devices. There are without doubt, in the 

 case referred to, assignable causes for such an undue increase. 



Coming back from this digression, the larvae of Acrony eta con- 

 tinued to feed during the entitle month of October before entering 

 into the pupa state. Asa matter of convenience, many were taken 

 home hy the writer, placed within a vivarium, and fed indiscrimi- 

 nately upon the leaves of various species of Polygonum, with 

 remarkable success. 



During the latter part of the feeding-time, there being a scarcity 

 of food plants in the immediate neighborhood in which he resided, 

 the thermometer indicating a rather low degree of temperature, 

 his charges were uncared for, and permitted to ramble about their 

 cage for days without suitable and wholesome nourishment. In 

 this predicament many passed into pupae. 



It is well known that the larva of this species constructs a 

 slightly spindle-shaped cocoon. To constitute a framework for 

 this essential covering, it places itself upon a small branch where 

 there is an abundance of leaves at convenient distances which it 

 unites by a perfect network of fibres, stretching from leaf to leaf, 

 or from stalk to leaves, lengthening and shortening as necessity 

 demands, until the desired configuration is assumed. Within this 

 structure, after the lapse of a definite period, it passes into a 

 chrysalis. 



Being a spinner of silk, this Noctuid approximates very closelj r 

 a Bombycid, the numerous members of whose family, with com- 

 paratively few exceptions, are cocoon-builders. So intimately 

 related to this family is the genus Acronycta, that it has been re- 

 tained in the tribe Bombycoides of Hubner. So important is the 

 habit of cocoon-manufacture, that it constitutes one of the chief 

 points of distinction between Nocturnal and Diurnal Lepidoptera. 

 For a species that has been proverbial for cocoon-making, any 

 marked deviation from what has been ordinarily observed, would 

 excite no little surprise, and, doubtless, would be accepted by some 

 who are slaves to their prejudices, with considerable hesitation. 



While the majority of my larvae of Acronycta passed through 

 their transformations in the normal manner, at least three without 

 the slightest attempt at cocoon-making, like the larva of Thyreus 

 3 



