152 Cuckoos and Hairy Caterpillars 



a forbidden food. But the domestic hen spoke a language they 

 couldn't understand, and her fussy duckings conveyed no warning. 



To return to the Cuckoo. The adults arrive in this country 

 about the middle of April, and are practically- all gone before July 

 is out. Their diet for some time after their arrival consists of insects ; 

 later on they appear to acquire the habit of eating hairy caterpillars 

 to some extent. But it is, I think, rather uncommon to find an old 

 bird distended with hairy larvae ; witli the young birds it is the rule. 



The Cuckoo's egg takes only 13 days to hatch, and the female 

 Cuckoos commence laving their eggs very soon after their arrival, 

 so that nestling Cuckoos are plentiful by the first week in May. 

 These nestlings will be able to fend for themselves by the end of 

 the month, and they at once start feeding on hairy- caterpillars. 



Cuckoos shot from the end of July to the beginning of October 

 are all young birds. During this period, a very large percentage 

 of birds examined will be found loaded with hairy caterpillars. 

 They eat smooth-skinned larvae too, but, as they are probably more 

 difficult to find, and do not generally exist in such large colonies as 

 the protected caterpillars, their choice commonlv falls upon the 

 latter. 



I do not know that there is any direct evidence on the point, 

 but it seems certain that Cuckoos must have the power of ejecting 

 from their stomachs the hairy residue, left after digestion of the 

 caterpillar, in the form of balls or pellets. It is inconceivable 

 that these bulky and valueless remains should be passed through 

 the whole length of the alimentary canal before being got rid of. 



Accepting the view that they cast out the hair in pellets, the 

 matter does not end there. In a large minority of birds examined, 

 the mucous membrane of the stomach is found to be lined with hairs, 

 not merely hairs that are lying in loose contact with the wall, but 

 actually embedded in the substance from which they can be drawn 

 out by a pair of forceps. Casual observers have supposed that the 

 Cuckoo's stomach was naturally lined with hair, but the microscope 

 proves that these embedded hairs are derived from the caterpillar. 



The rhythmical movements of the stomach during digestion 

 cause the contents to move in certain definite lines, pressing the hairy 

 bolus against particular areas of the mucous wall. The hairs, or a 

 number of them, penetrate the epithelium and become arranged in a 

 regular spiral form over the interior, and we have the appearance 

 of a stomach growing a thick crop of hair. 



This subject, even now, is very' imperfectly understood, I think. 

 Numerous questions present themselves which cannot be answered 

 with our present knowledge. 



What, for instance, is the ultimate fate of these embedded hairs ? 

 Are they shed after a time, leaving the bird with a clean, mucous 

 surface ? How far does the hairy lining interfere with the normal 

 process of digestion ? Do the implanted hairs actually take root 

 and grow in their new situation ? Finally, is it not probable that 



