NESTLESS BIRDS AND ANNEXERS 57 



their foster parents and depositing their own eggs in 

 them. Of course the parents of these deserted young 

 birds might simultaneously assist in the development 

 of the parasitic habit ; for it is quite conceivable that 

 with a brood of voracious young to provide for, they 

 might readily desert some or even all of them, and 

 more especially if they chanced to observe the readi- 

 ness of other species to share their labours. So in 

 both directions would the domestic instinct or habit 

 gradually become weaker and finally disappear, whilst 

 parasitism would as surely take its place. By tracing 

 the origin of this avine parasitism through the young 

 rather than through the adult, we are better able 

 to understand that marvellous perfection of choice of 

 foster parent now exhibited by all parasitic birds, the 

 species selected being those that are in every way 

 best adapted to secure its ultimate success. We 

 believe that Dr Baldamus (a naturalist who has 

 studied this habit of the Cuckoo perhaps more 

 thoroughly than any other) attributes parasitism to 

 the fact that the Cuckoo produces its eggs at such 

 long intervals that one general incubation would be 

 impossible ; but on the other hand we must take into 

 consideration that other species of non-parasitic birds 

 lay at intervals, and begin to sit as soon as the first 

 egg is produced ; whilst it is much more probable 

 to assume that intermittent egg-production in the 

 cuckoo is a direct result of the bird's parasitic habits. 

 Incidentally I may mention that a most interesting 



