Professor Owen on Metamorphosis and Metagenesis. 271 



Most insects quit the egg' in the form of a worm, which 

 masking, as it were, a different and higher form, is called 

 the " larva ;" it is active and voracious, — but usually falls into 

 a kind of torpor during which the changes take place which 

 issue in the flying insect ; during the passive stage of meta- 

 morphosis it is called a " pupa ;" the last volant stage is the 

 *• imago.** 



The chief steps in the metamorphosis were traced as they 

 affect the outward form, the digestive organs, the circulatory, 

 and respiratory, and nervous systems. 



The main differences in the metamorphoses of insects re- 

 late to the place where, and the time during which they are 

 undergone. The young cockroach and the little aphis, which 

 were first acephalous and apodal, and had then thirteen equal 

 segments, with soft unjointed legs, proceed to acquire a dis- 

 tinct head with antennae, a thorax with three pairs of long 

 jointed legs, and an abdomen, before they quit the egg ; they 

 thus enter upon active life under the guise of a crab, instead 

 of a worm. With regard to the Aphis ^ that insect, instead 

 of proceeding to perfect its individual development, may at 

 once begin the great business of its existence by parthe- 

 nogenetic procreation. Bonnet's experiments, which first 

 brought to light this marvellous fact, have received uniform 

 confirmation from all subsequent inquirers, and no natural 

 phenomenon is now better determined. 



From seven to eleven successive generations have been 

 traced before the individual has finally metamorphosed itself 

 into the winged male or winged oviparous female. 



In autumn, when the nights grow chilly and long, the ovi- 

 parous imago completes her duty by depositing the eggs in 

 the axils of the leaves of the plant, where they are protected 

 from the winter frost, and ready to be hatched a-t the return 

 of spring. Then recommences the cycle of change, which 

 being carried through a succession of individuals and not 

 completed in a single life-time, is a "metagenesis" rather 

 than a *' metamorphosis." 



This phenomenon which, until very recently, was deemed 

 an exception, and a most marvellous one, in Nature, now 



