210 BRITISH BIRDS. [vol. xiii. 



to inspection, and from the 26th day the young feed directly 

 from the deep probings made by the adult. In the 5th week 

 the bill of the chick begins very visibly to assume the adult 

 form. Definite tentative probing (probing mainly or entirely 

 by touch) appears in the 5th week, and at first meets with 

 little success. Often only cinders are retrieved. Circular 

 leverage is the last act of the motor repertory connected 

 with probing to appear. But in probing the chick still falls 

 far behind the adult in vigour, rapidity, and certainty, and 

 at the 35th day is not by any means able to feed itself by 

 probing in the ground. 



Since the egg-tooth persists and the bill remains unpolished 

 for the first six days, and the characteristic feeding reactions 

 of the species do not begin to appear until well on in the 

 2nd week, and true tentative probing is not seen until the 

 5th week when for the first time the bill approaches the 

 definitive adult form, the assumption seems justified that 

 the development of the bill in ontogeny differs from that 

 followed in its phylogeny. The developmental stages of the 

 bill in the individual have no adequate feeding mechanisms 

 associated with them, which is what one would expect to 

 be the case if the growth of the bill in the individual repeated 

 its history in the species. 



On the sensory side the feeding activity evolves from 

 probing dependent on the visual factor to probing in which 

 the sense of touch becomes more directly important than 

 vision, which is relegated to the selection of suitable feeding 

 places. It is remarkable that the process of acquiring the 

 tentative probing habit should persist, since the successes 

 at first and for some time are limited. 



In another way the results are of interest. The highly 

 specialized motor activities involved in opening up marine 

 littoral shellfish, characteristic of the Oystercatcher, are 

 shown to perfection by the last stage (?) chick reared entirely 

 in an inland habitat. These activities appear as " play." 

 In the 5th week the chick spends much time hammering at 

 old tree stumps when these are available and levering off 

 fragments of rotten wood. The chick acts precisely as it 

 will do later in opening up mussels and other bivalves on 

 the coast, though a considerable difference is manifest in 

 the vigour, speed and control of the act at five weeks and at 

 four months. 



Affective States. — Jerking the head and tapping the 

 ground, characteristic reactions of waders generally, appear 

 as early as the 6th day, and are an indication of excitement. 



