54 



lesser alterations are frequent : for example, in parts, at least, 

 of the northern districts of England, the common brimstone 

 moth is single-brooded ; indeed, cases of this kind are far 

 from ixncommou, 



VAEIETIES IN THE PERFECT STATE, 

 A. — TSTOEMAL TAEIATIONS. 



1. Sexual. — Almost all insects vary somewhat in the two sexes, 



but some, as Sypogymna Dispar, vary so extremely that they 

 might well be taken for different genera. Secondary subjects 

 of interest arise from a consideration of these sexual differences : 

 for example, the more pectinated antennae in the male seem 

 to point to these organs as connected with the function of 

 smell ; again, the apterous condition of some female moths is 

 worthy of note, as also the fact that this wingless state is 

 so very prevalent amongst our winter insects, 



2. Local varieties. — 



a. With regard to size alone. 



h. With regard to colour or markings. 

 Many insects are decidedly smaller in the northern parts of our 

 island than in the south. Simera pennaria affords one 

 example. Of changes in colour many proofs also may be 

 found without resorting to the more doubtful ones, such as 

 CcenonymjjJia Typhon and Polyommatus Artaxerxes ; Xylopliasia 

 lithoxylea, X.polyodon, and Grapholita ulicetana give examples 

 admitting of no cavil, 



3. Spring and Autumnal varieties. — As in the genus Pieris, the 



true thom-inoths, &c. Here it must be noted that some 

 insects appear twice in the year, but that the autumnal brood is 

 not parent to the brood of the following spring, such, 

 aecordmg to my experience, is the case in the genus Lasiom- 

 mata. These three classes of varieties seem to be more or 

 less constant, and may be termed natural varieties ; the 

 remainder obey no law, and we shall therefore call them 

 abnormal, 



B. — ABNOnMAL VAEIATIONS. 



1. Varieties of frequent occurrence, but not apparently depending 

 on local causes — Abundant examples of this group may be 

 found, as in Apamea oculea, Peronea, &c. The much greater 

 tendency of some species to vary is remarkable. 



