THE YOUNG 



NATURALIST. 



3 



EFFECTS OF FOOD IN PRO- 

 DUCING VARIATION. 



Various theories are put forth from time 

 :o time in the endeavour to account for the 

 /ariation of colour or markings on the wings 

 Lepidoptera. One person feeds his larvae 

 ilways on the same food and produces 

 varieties, he jumps to the conclusion that 

 he result is owing to the uniformity of diet. 

 Mother, changes the food continually and 

 )rocures varieties. He concludes that the 

 onstant change has made the difference. 

 Both these cases are instances of a conclu- 

 ion being arrived at without the premises 

 •teing sufi&cient. The very fact that such 

 'pposite opinions are held is a proof of the 

 isufiicency of the evidence. Mr. Gregson 

 ^ one of the most successful variety breeders 

 a the case A. grossiilariaia, and it is said 

 hat he accounts for his success because he 

 i ontinually introduces a new strain into his 

 olony of the insect. This would seem to be 

 le most unlikely way of obtaining a succes- 

 ion of varieties, for the introduction of 

 new blood" from the normal form of the 

 pecies would certainly tend to bring back 

 de race to its former position, and the 

 hange that had been made would be lost, 

 ome species are remarkably constant to 

 le type, yet it often happens in such a 

 pecies that a well marked variety occurs, 

 ither locally, or generally. On the other 

 ; and, others are variable to a very great 

 " xtent, e.g. grossulariata and caja; yet neither 

 •I f these, nor any other very variable species 

 as succeeded in producing a permanent 

 reW marked form. There are certain tcn- 

 : encies in variation, of which scarcely 

 nough notice has been taken. Reds have 

 tendency to vary to yellow ; yellows have a 

 •ndency to become white ; other colours vary 

 .,utin intensity as a rule, becoming lighter 

 , r darker, but not changing in hue. All the 

 Jumets produce varieties with yellow spots 

 istead of red ; and some European species 

 /hich are banded with red, produce varieties 



with yellow bands. This is like the red- 

 banded Clear wings, which sometimes pro- 

 duce varieties with yellow bands. The 

 Jersey Tiger C. hera, has a well known 

 variety with yellow hind wings. Our more 

 abundant Wood Tiger has red markings on 

 the body of the female, while the yellow of 

 the wings is changed to white in the variety 

 Hospita. In the Common Tiger the tendency 

 of the red to change to yellow is often very 

 marked. If we go abroad the illustrations 

 might be greatly increased in number. On 

 the other hand, greens never vary to blue, 

 nor yet to yellow, nor do these hues change 

 in other directions. Next to these changes, 

 the more important variations are produced 

 by a greater or less preponderance of some 

 colour already included in the hues of the 

 normal form. Thus the var. Combusta is 

 produced by the brown shade spreading 

 over a larger portion or the whole of the 

 wing. Piceata and many other named forms 

 are from the same cause — the dark scales 

 predominating. The reverse is the case in 

 Albinos, or specimens with a tendency in 

 that direction ; the white or pale scales are 

 more numerous. Melanism is perhaps the 

 reverse of this, but sometimes black varieties 

 appear in insects that have no black in their 

 colouration. Polydon, for instance, has at 

 best dark brown scales — none truly black — 

 yet very black specimens are not unfrequent. 

 These are but crude thoughts, more to raise 

 a discussion than settle any point ; but if 

 food has such varied results in certain cases, 

 why not in other cases, and why not an 

 uniform effect. Is it not more probable 

 that there are certain laws affecting variation 

 that might be discovered by careful study 

 and examination of a large number of 

 specimens and species. It seems very 

 doubtful whether food has any effect on 

 colour ; and we cannot help thinking of 

 Gulliver's spiders, and how their keepers 

 managed to have spider's webs of any 

 colour they desired. 



