SDctotier 



XXXIX 



There is one rule to which, although it has escaped 



the observation of many persons who feel a 



"^ '■ Gossamer 



warm general interest in animated nature, 



there is no exception. That rule enacts that no insect 



can add to its stature once it has passed the stage of 



larva (grub, maggot, or caterpillar) and has become a 



pupa (chrysalis or cocoon). 



' But,' one may hear an incredulous person argue, ' is 

 not the common house-fly an insect ? ' 



' Undoubtedly. It has a segmented body, six legs 

 and breathes through tracheae or air-tubes instead 

 of lungs.' 



'Very well,' persists the sceptic; 'look at that 

 window. Are there not house-flies of three or four 

 different sizes on the panes ? ' 



' Certainly ; but the smaller flies are not the young 

 of the larger ones. I see on that window flies of three 

 or four different species, though I am not doctor enough 

 to distinguish them by name. They bear a strong 

 resemblance to each other; but you may rely on it 

 that all the individuals of the same species and sex 

 are of the standard dimensions assigned to that species, 



213 



