Cocoons, Nests and Eggs 



which it is deposited is girdled, to prevent further growth 

 which would assuredly crush the egg. The manner of 

 depositing eggs, the situations in which they are laid, and 

 the form in which they come into the world are all of the 

 greatest interest. 



As we shall see, eggs which are destined for an aquatic 

 life are usually covered with a layer of jelly-like substance 

 after the manner of frog spawn. Eggs laid on a tree may 

 either be on its surface, as in the case of the rings of eggs 

 deposited by the lackey moth, or actually in its tissues, 

 as in the case of the cicada. Some eggs, those of 

 mosquitoes, float on water ; others, those of lacewings, 

 wave on stalks in the air ; some are preserved from injury 

 by horny coverings, others are laid in great masses and 

 protected by substances derived from the body of the 

 mother. One thing is certain, the mother always does 

 her best that her labours may not be in vain even if she 

 omits to mother her young. 



Some very interesting experiments have been carried 

 out on this subject, of which we can but give the barest 

 outline here. Taking the common cabbage-white butter- 

 fly as our example : it is well known that this insect will 

 only lay its eggs on cabbages or on closely related plants, 

 and with a reason these plants and these alone form 

 suitable food for the cabbage-white larvae. Now all these 

 plants possess a substance which gives them their 

 characteristic odour, and this substance can easily be 

 extracted. Taking some of the substance and smearing 

 it on a piece of sacking, cabbage-white butterflies were 

 easily persuaded to lay their eggs thereon, despite the fact 

 that the larvae could not possibly feed on sacking. Similar 

 experiments were carried out with other substances and 

 other insects with like results, showing that the sense of 

 smell probably guides the mother insects in their choice 

 of a site for their eggs. Be that as it may, it is wonderful 

 that the adult insects, which sip the nectar of flowers, should 

 know on which plants they may or may not lay their eggs. 

 G 97 



