AND THE LOWER ANIMALS. 81 



tracted that it hardly extends over five of the larval 

 rings. But, as it were to compensate for this, the 

 eyes, proboscis, antennae, feet, and wings, have been 

 added to the outer surface, and important anatomical 

 changes have also taken place within. The larval skin, 

 which thus forms a sort of shell for the pupa, being in 

 great part empty, floats upon the surface of the water. 

 After five or six days the nymph begins to move about 

 in this case, which incloses it ; and finally the latter 

 bursts above, and the stratiomys, disengaging its limbs 

 of their envelopes one by one, springs from its floating 

 cradle. More fortunate than most aquatic species, it- 

 is incapable of being submerged, and consequently has 

 little dread of shipwreck ; and it is whilst treading as 

 securely upon water as on land that it casts off the last 

 garments in which it had been enswathed. 



Leaving the Diptera, we find only insects which 

 have incomplete metamorphoses, or none at all. It 

 is usual to state this fact alone, but the generally 

 accepted notion that we ourselves are developed in 

 obedience to the same general principles as those 

 which control the formation of insects, allows us to go 

 a step further, and to regard all these modifications, 

 and even the entire absence of the phenomenon, as the 

 result of two immediately distinct causes, or at least 

 as the products of two very different processes. The 

 incompleteness of the metamorphoses may be due either 

 to a premature development of the insect while within 

 the egg, or to an arrest of development after it has been 

 hatched. The entire absence of metamorphoses is 

 owing to the influence of these two causes combined. 



The Orthoptera, including the grasshoppers and 

 crickets, and the Hemiptera, embracing the bugs, 



G 



