>24- 



LETTER XXX. 



To the same. 



SELBORNE, April yd, 1776. 

 EAR SIR, Monsieur Herissant, a French 

 anatomist, seems persuaded that he has 

 discovered the reason why cuckoos do not 

 hatch their own eggs ; the impediment, he 

 supposes, arises from the internal struc- 

 ture of their parts, which incapacitates them 

 for incubation. According to this gentleman, 

 the crop, or craw, of a cuckoo does not lie before the sternum 

 at the bottom of the neck, as in the gallince columbce, &c., but 

 immediately behind it, on and over the bowels, so as to make 

 a large protuberance in the belly. * 1 



* " Histoire de 1' Academic Royale," 1752. 



1 There is nothing whatsoever in the structure of the cuckoo to prevent 

 its hatching its own eggs. The whole question of the curious parasitism 

 of cuckoos and some other birds (such as Molotkrus) has since been fully 

 elucidated by Darwin. ED. 



