244 NATURAL HISTORY. [CH. XVI. 



feed and grow, we are convinced that the larva 

 state of the hippobosca must have been undergone 

 previous to the assumption of this form, and conse- 

 quently previous to its being deposited by the fe- 

 male fly. And the statement of Reaumur, that the 

 outer envelope of this egg is nothing else than the 

 hardened and contracted skin of the larva, is a cor- 

 roborative of this opinion. Reaumur adds, that 

 when the perfect insect escapes from its oviform 

 case, it is the exuvia of the pupa which it leaves 

 behind. The researches of Degeer, however, prove 

 that it is not only the exuviae of the pupa, but also 

 the indurated skin of the larva, which is thus quitted, 

 this author having opened one of the cases and 

 found the real pupa enclosed, having the legs clearly 

 folded over the breast, just as in the fleshflies, and 

 in any other dipterous insects. It was only by the 

 most unwearied assiduity that these distinguished 

 authors arrived at a knowledge of the true nature 

 of these curious insects, and for the purpose of 

 showing the zeal which enabled them (and which 

 alone can enable others who would tread in their 

 footsteps in similar pursuits), to overcome the great 

 difficulties attending the necessary investigations, 

 it may be mentioned, that after the servants of 

 Reaumur had with great diligence found him fe- 

 male flies ready to deposite their burdens, so anx- 

 ious was he to observe their transformations, that, 

 in order to secure to them the natural warmth 

 which they enjoyed upon the body of the horse, he 

 carried them about in his pocket by day, and actu- 

 ally took them to bed with him by night, for several 

 weeks. 



The hardness of this cocoon, as we must now 

 regard it, proves of the greatest service in defend- 

 ing the enclosed insect against the attempts of the 

 animal upon which it is deposited, to injure it. It 

 might, however, seem at first likely to obstruct the 

 escape of the enclosed insect when ready to burst 



