1864.] 415 



color of their pencils and not in their location, and the imagos are iden- 

 tical, it may well admit of a question whether they are not mere Phy- 

 tophagic Varieties. It became desirable therefore to test this point in 

 the manner recounted below, the principles of which it will be neces- 

 sary first to explain. 



When a species feeds indiscriminately upon several plants, individu- 

 als, that have fed for a certain period upon one of those plants, may be 

 shifted upon another of the plants that they commonly feed on without 

 injury to their health. I have done this in so many different cases 

 with Lepidopterous larvae, that I believe that, in their case at all events, 

 it is a general law. For example, it is a common practice in England, 

 and I have repeatedly done so when a boy, to feed the common silk- 

 worm when it first hatches out on lettuce leaves, and afterwards to 

 change its food to mulberry leaves. Yet the insect thrives just as well, 

 and spins up just as certainly under this treatment, as if it had been 

 fed on mulberry leaves throughout. Lepidopterous larvse will even 

 sometimes voluntarily shift, from a plant of one family to another of a 

 very widely distinct family. Several years ago I had, in the same cage, 

 about a score half-grown larvae of Spllosoma virginica Fab. feeding on 

 apple leaves, and by the side of them several larvae of Pyrameis hun- 

 tera Sm. Abb. feeding on sunflower leaves. To my great surprise the 

 former all suddenly quitted the apple-leaves for the sunflower-leaves, 

 and I finished them on that plant and they, most of them, developed 

 next year into the imago. 



In confirmation of these views, Mr. Edwards, to whom I had refer- 

 red for his opinion on this subject, writes to me as follows : — " I have 

 often found that where I had one larva, say of excsecata, from the 

 elm and another of the same from the cherry, and put food for both in 

 the same vase, the two would be probably both of them on the cherry 

 soon after. I have often changed the food-plant, when the one on 

 which I found a larva was inconvenient to procure, for one nearer the 

 house that I knew it liked. I have collected larvae of Limacodes from 

 oak, hickory, wild cherry and cherry, and have put the lot on a hickory 

 or oak near my house. They did just as well." 



On general principles, therefore, if Antlphola and fessellaris were mere 

 Phytophagic Varieties, and not Phytophagic Species, it must be obvious 

 that it would be possible to feed tessellarls on oak-leaves and Antlphola 



