iS94. FURTHER NOTES ON INSECTS. 369 



coccids every day. The caterpillar is short and stumpy in shape, 

 tapering towards the head, and recalling in appearance the maggots 

 of some flies. Only the three hinder pairs of pro-legs are functional ; 

 those on the fifth and sixth abdominal segments are used for walking, 

 the hindmost pair being attached to the case, which they keep in 

 position. When fuU-fed, the caterpillar chooses a crevice in the 

 bark or a fork between two branches, where it fixes its case, spins a 

 cocoon, and pupates, having first taken the precaution to gnaw an 

 aperture through which the moth can come out. So rapid is the 

 transformation, that four or five broods follow each other during the 

 summer. The execution upon the coccids must, therefore, be very 

 great, and Professor Riley states that it is intended to import the moth 

 into California, where it is hoped that it may prove as serviceable as 

 the other predatory insects which have been introduced there to make 

 war upon the destroyers of the fruit-trees. 



After discussing carnivorous caterpillars. Dr. Seitz gives instances 

 of the habit of nest-making which some caterpillars practise, living 

 in colonies, with the web spun by their united labour as a protection. 

 The influence of the food of the larva upon the colour and size of the 

 imago is next considered. Some observers have thought that the 

 sex of the moth is aff"ected by the food of the caterpillar, poverty of 

 nutriment producing males ; but Dr. Seitz points out that the fact on 

 which this rests — that some neglected larvae of a batch pupating 

 early produced males, and the rest, fed afterwards, females — is better 

 explained by supposing a tendency to an earlier development of 

 males, or proterandry (if a botanical term may be borrowed). There 

 can be little doubt that the sex is irrevocably fixed in the egg. The 

 difference of feeding by which bees can rear a worker or a queen at 

 will is not, of course, an instance of determination of sex by food, 

 as the worker is only an infertile female. 



Dr. Seitz discusses also the causes which govern the time of 

 development of a species, pointing out the advantage of rapid growth, 

 when climatic conditions permit, in giving rise to several broods, and 

 thus enormously increasing the number of individuals. The relation 

 between caterpillar and imago, as regards size, is of considerable 

 interest, the body of the latter being in some cases much smaller than 

 that of the former, while in others the difference is less marked. In 

 some moths we find a complete division of labour between the larval 

 and perfect stages, the former being entirely devoted to feeding, the 

 latter to reproduction. In such the mouth-organs of the moth, which 

 lives but a few days, are vestigial. Dr. Seitz suggests that, as this 

 condition exists in some of the most primitive families (Cossidse, 

 HepiaUdae), these may have come down to us unchanged from a 

 period anterior to that of honey-bearing flowers. In some of the 

 highest moth-famihes, however (Saturniidae, Arctiidae), we find the 

 same state of things, and it seems more likely that in all cases it is a 

 degradation and not a survival. A review of the habits of the butter- 



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