STATES OF INSECTS. 287 



way out at that end, and then by moving its legs, the 

 cases of which in some species are ciliated for this very 

 purpose, swims to the surface, where its skin splits, and 

 discloses the included insect. That these jaws are given 

 for the express and exclusive purpose of being thus ap- 

 plied, seems undeniable. The pupa eats nothing — they 

 are therefore in every other point of view superfluous. 

 They are given to it alone of all other similar pupae, be- 

 cause unnecessary to all others; and they are cast off 

 along with the rest of the puparium, the perfect insect 

 having no vestige of jaws a . 



The gnat has to undergo its change on the surface of 

 the water — How is it to accomplish this without being 

 wetted ? In the pupa state they usually remain suspended 

 with the posterior end of the body turned downwards : 

 but when the period for its change is arrived, it stretches 

 it out upon the surface, above which its thorax is elevat- 

 ed. Scarcely has it been a moment in this position, than, 

 swelling out the interior and anterior parts of the thorax, 

 it causes it to split between the two respiratory horns. 

 Through this opening the anterior part of the gnat then 

 emerges. As soon as the head and trunk are disengaged, 

 it proceeds with its labour, and gets out more and more; 

 elevating itself so as to appear in the pupnrium like a 

 mast in a boat. As it proceeds, the mast is more and 

 more elevated and lengthened, till it becomes nearly per- 

 pendicular — just as the mast of a boat is gradually raised 

 from a nearly horizontal to a vertical position : at this 

 period a very small portion of the abdomen remains in 

 the puparium. Neither its legs nor wings are of any use 



" De Geer ii. 519. 



