May 



parasitic. A second species always lays its eggs in 

 the nests of strangers, with an occasional exception, 

 when several together build a rough nest in some 

 ill-adapted situation. They often lay so many eggs 

 fifteen to twenty in the foster nest, that few or 

 none can possibly be hatched. They also lay many 

 eggs upon the ground. A third species lays its 

 eggs singly in the foster nests, the young birds 

 being securely reared. 



\5"hat there is nothing unique in the parasitism 

 of our cuckoo will appear from the fact that there 

 are several other species of cuckoos well known to 

 be parasitic ; and, similarly, any deviations from the 

 parasitic instinct on the part of our bird, such as the 

 reported laying of its egg on the ground, sitting 

 upon it, and feeding its young, would appear to 

 be only a partial reversion to a former state of 

 things in which it performed its natural duties, just 

 as they are performed to this day by the normally 

 non-parasitic American cuckoo. 



It would, therefore, appear that our bird has 

 passed through stages of less perfect parasitism 

 similar to those described above, the question 

 remaining to be solved being How came it to 

 attain to that perfection of degeneracy which it 

 now exhibits, having abandoned duties which rest 

 upon the deepest instincts governing the life of 

 birds ? 



There are certain sets of correspondences between 

 the structure of the cuckoo and its young and the 



149 



