INTRODUCTION. 19 



which certain generations are viviparous without any- 

 sexual process.* It has been said that insects as a rule 

 are oviparous though they may be viviparous. Some- 

 times the larva is so far developed within the maternal 

 oviduct, as to be almost ready to enter on its second or 

 pupal existence on its appearance into the world. 



Insects, as a rule, in their development from the egg, 

 undergo, as is well known, a series of changes called 

 metamorphosis ; this is sometimes very complete or in- 

 complete, and sometimes there is no change of form. 

 As instances of complete metamorphosis I may mention 

 butterflies, moths, and beetles, which go through 

 three distinct stages called the larva, pupa, and imago, 

 or perfect state. In the first stage the insect is like a 

 grub, either provided with legs or destitute of those 

 organs; in common language we call them caterpillars, 

 maggots, or grubs; during this period eating is the 

 order of the day, and this they do generally very vora- 

 ciously, and in many cases most injuriously to the 

 cultivated products of the soil. After repeatedly- 

 changing the skin to allow of the creature's growth, for 

 the skin does not grow with the body, it assumes the 

 pupa, or as it is usually called amongst butterflies and 

 moths, the chrysalis stage. Here is perfect quiescence, 

 the creature neither moves nor eats ; there is death-like 

 repose for a period, more or less long, according to the 

 species. But though externally no change is visible, a 

 wonderful drama is being acted "behind the scenes," 

 and in due time that which entered the pupa state a 

 grovelling grub emerges from it a beautiful winged 



* See Rolleston's " Forms of Animal Life." cxii. 



C 2 



