58 PRIZE ESSAY : 



appears to assign to each species one or more destructive para- 

 sites, which prey upon them during all stages of their existence. 

 "Were it not for this wise provision, some of the most prolific and 

 hardy tribes, being exclusively vegetable feeders, would prevail 

 to the exclusion of all others. The Hessian fly has numerous 

 parasites, which have been studied with marked success by Mr. 

 E. C. Herrick. Mr. Herrick's papers, published in the "Amer- 

 ican Journal of Science," (vol. XLI.,) and in the Patent Office 

 Reports for 1844, are most favorably spoken of by Dr. Fitch, 

 who states that these papers evince the close and patient investi- 

 gation which the writer has made, and the utmost carefulness in 

 announcing nothing beyond what he had clearly ascertained. 



95. In Dr. Fitch's essay, published in 1846, he introduces the 

 following brief sketch of that part of Mr. Herrick's papers on 

 the Hessian fly, which relates to parasites : 



" The Hessian fly is preyed upon and devoured by at least four 

 other insects. When its eggs are layed upon the wheat leaves, 

 they are visited by an exceedingly minute four-winged fly, a spe- 

 cies of Platygaster,) which punctures the egg, and deposits in it 

 four or six eggs of its own. The Hessian fly worm hatches, 

 grows, and passes into the flax-seed state, with these internal foes 

 feeding upon it. It now dies, and its destroyers in due time es- 

 cape from the flax-seed shell. Three other minute four-winged 

 flies, or bees, as they would be called in common language, de- 

 stroy the fly when in its flax-seed state. The most common of 

 these, by far, is Say's ceraphon destructor. Alighting upon the 

 wheat stalks, ins-tinct informs them precisely where one of these 

 flax-seeds lies concealed. They thereupon ' sting' through the 

 sheath of the stalk, and into the body of the worm, placing an 

 egg therein, which hatches to a maggot, lives upon and devours 

 the worm.'' 



96. " Such are the means which nature has provided for pre- 



