CH. XVI.] DIPTEROUS INSECTS. 245 



forth, weak as it must necessarily be upon assuming 

 the winged state. 



Here, however, we find the difficulty overcome 

 by one of those beautiful instances of precaution 

 which are nowhere more manifest than in the in- 

 sect world. The rounded tip of the cocoon cor- 

 responds with the head of the fly, and resembles a 

 scuUcap, divided into two equal portions, the union 

 of which with the remainder of the cocoon is 

 marked by a faint line, perceptible only by the as- 

 sistance of a magnifying-glass. The insect, there- 

 fore, upon pushing against this cap with its head 

 from within, causes it to fall off, whereupon the fly 

 creeps forth in its winged state, and immediately 

 commences feeding upon the animal upon which it 

 was deposited by the parent fly. We will only fur- 

 ther mention that the true larva of this insect has 

 not yet been observed, and that it is most probably 

 nourished in the abdomen of its parent by the blood 

 of the horse, of which the latter takes such copious 

 draughts. It would moreover prove a curious sub- 

 ject for investigation in a physiological point of 

 view, to ascertain the real egg-state of the insect, 

 and to discover what becomes of the exuvia of the 

 egg after the insect has burst forth. We trust that 

 some patient inquirer will endeavour to supply 

 Jhese interesting links in the history of the forestfly 

 X I* 



