1218 THE BUTTERFLIES OF NEW ENGLAND. 



Desiderata. No oue lias attempted as yet to trace tlie limits witliin 

 which this species is digoneutic, as it appears to be throughout Europe. 

 Probably it is so in the White Mountain region of New England and in 

 the more northern limits of its range ; southwardly it probably becomes 

 polygoneutic and the separation of the broods would be difficult. It 

 might, however, be possible to trace the southern limits of trigoneutism. 

 The forward march of the species in the extreme south and west merits 

 immediate attention and the rapidity with which its parasites find it out. 

 The variety hovangliae invites close study ; every instance of its occurrence 

 (and abundance) should be noted, giving date and place, and, when known, 

 the food plant of the caterpillar which produced it. Is it now found at all 

 commonly in regions invaded by R. rapae within five years ? Does the 

 caterpillar feed of its own choice on Tropaeolum, and if not will hunger 

 induce it to do so? Do any of our native parasites, not also found in 

 Europe, attack the caterpillar, or the egg? 



LIST OF ILLUSTRATIONS.— PIERIS RAPAE. 



Egg. Imago. 



PI. 65, fig. 28. Plain. ^'' "'^ ^K- H- !'• '• novangliae, S , both sur- 



68 : 16, 17. Micropyle. faces. 



12. P. r. rapae, S , both surfaces. 

 Caterpillar. 16 : 4. Female, upper surface. 



PI. 72, fig. 4. Caterpillar at birth. ^- Male, upper surface. 



76 : 11, 12. Full grown caterpillar. ^5 : 10. Male abdominal appendages. 



79:53. Head, fifth stage. *6 = ^- Androconium. 



86:31. Prolegs. 61-^2. Papilla of tongue. 



36. Glandular swelling of first thoracic General. 



segment. P1.88,fig.l2. Apantelesglomeratus, a parasite. 



43. Dermal appendage, first stage. 89:1-2. Pteromalus puparum, a parasite. 



13-15. Exorista hirsuta, a dipterous 

 parasite. 



Chrysalis. 



PI. 84, fig. 58. Side view. Map of distribution in North America 



65. Dorsal view. from 1860 to 18S6. 



