406 SYSTEM OF INSECTS. 



a variety ; for those characters that in some are con- 

 stant, in others vary. In general, where there is no dif- 

 ference inform^ appendages and organs^ sculpture^ propor- 

 tions and larvce, colour alone, especially in insects in- 

 habiting the same district, only indicates a casual variety. 

 Thus Aphodius luridus has sometimes pale elytra with the 

 striae Wack*(Sc0ro&rws nfro-sulcatus Marsh.): at others it 

 has black spots between the striae, as in the type : in a 

 third variety the elytra are black at the base and pale at 

 the apex (Sc. varius Marsh.) ; and lastly, in a fourth they 

 are intirely black (Sc. gagates Marsh.); yet all these in 

 every other respect precisely correspond. But the con- 

 verse of this will scarcely hold good ; for doubtless minor 

 differences of structure are sometimes produced by a 

 different food and climate : which may probably account 

 for some variations observable in the individuals appa- 

 rently of the same species obtained from different coun- 

 tries. 



Having considered the kind and value of the groups 

 into which Annulose animals, and more especially insects, 

 may be divided, I shall next call your attention to their 

 composition. There are Jive numbers and their multi- 

 ples which seem more particularly to prevail in nature : 

 namely, Two Three Four Five and Seven. But 

 though these numbers are prevalent, no one of them can 

 be deemed universal. The binary number, which af- 

 fords the most simple, and for that reason perhaps not 

 the least valuable, mode of arrangement, we see exem- 

 plified when two branches, so to speak, diverge from a 

 common stem, as in the Vegetable and Animal king- 

 doms ; the terrestrial and aquatic Predaceous beetles; 



