430 



PHYSIOLOGY. 



in the air by means of the first strikings of its wings, which succeed 

 but imperfectly, and it then seeks a more elevated spot whence to 

 exercise its new function with fuller effect. 



Some genera, which from their abode in water prior to this period, 

 make a transition to living in the air, form in a remarkable manner a 

 perfect exception to the law, that with the casting of the pupa case the 

 metamorphosis of the individual is concluded. It is universally known 

 of the Ephemera, that in about half an hour, and indeed frequently 

 only some minutes, after they have quitted the pupa case, again moult, 

 and then only are able to copulate and procreate. This observation 

 may be repeated without the least trouble in July and the commence- 

 ment of August, when the Ephemera in watery situations quit the 

 water towards evening by myriads. The just excluded Ephemera 

 nutters immediately, although with difficulty, out of the water, and in 

 the course of a quarter or half an hour, but in the smaller species in a 

 shorter space of time, it seeks an elevated object, for instance the stem 

 of a tree, the post of a bridge, houses that are close at hand, and 

 even individuals standing upon the bank, and here clings firmly with 

 extended legs. Speedily afterwards the dorsal case splits in its middle, 

 upon which the insect with violent motion first frees its head and 

 anterior legs from the old skin, which is succeeded by the other legs as 

 soon as the anterior ones have affixed themselves, and then at the same 

 time, but gradually, by the wings and abdomen. Prior to this moult- 

 ing the creature has not acquired its usual markings and dark colour, 

 which we perceive immediately after the new change of skin ; and it is 

 also remarkable, that after this change all the limbs, particularly the 

 longer anterior legs and anal setae of the male, become both more 

 slender and longer than before. The horny case of the eyes is the only 

 part which does not participate in this moulting. An analogous pro- 

 cess is found to take place in the pupa of the Phryganecc and Semblodes, 

 which in that state repose without taking food, and are consequently 

 endowed with a perfect metamorphosis, for, according to De Geer *, it 

 quits its place of repose, beneath the water, and creeping up the sides 

 higher than the surface, there casts its pupa case. I am inclined to 

 surmise from my own, indeed not fully comprehensive observations, 

 that the already perfected insect creeps forth, and then reposing for a 

 time, moults a second time. During this repose the wings especially 



f- M^moires sur I'Hist. des Insectes, torn. ii. 



