212 BRITISH BIRDS. 



indistinguishable from old ones, except by its first two 

 primaries. 



Dr. Bureau points out that the figures in this table 

 are average ones, based on a large number of actual 

 measurements; they therefore represent the normal 

 development of a young Partridge with very fair 

 accuracy, so that if any individual is found to exhibit 

 any marked deviation from the figure given in the table, 

 it is extremely probable that the particular bird is behind 

 or in advance of the normal development for its age. 

 The amount of this variation also can easily be deter- 

 mined by comparing the lengths of the last new primary 

 and that of its internal neighbour with the figures in the 

 " Chronometric Table," and may be summed up thus : 

 " A young Partridge in which a growing primary is 

 longer than the average at the time that its external 

 neighbour is shed is probably a backward bird, and 

 vice versa, where it is shorter the bird is a forward one." 

 The possible errors from this variation in development 

 are given by the author in a table on p. 40 and are 

 shown to be within very narrow limits — viz : between 

 one and two days either way in the case of the tenth to 

 the fifth primaries, and three days either way in the case of 

 the fourth and third ; when, therefore, the whole period of 

 110 days is taken into consideration, the amount of 

 possible error is for practical purposes negligible, more- 

 over extreme cases are quite rare. 



On page 16 will be found the table giving the rate of 

 increase in twenty-four hours of each first winter-plumage 

 primary, and from this it will be seen that the tenth 

 grows the fastest (5.5mm. per diem), the ninth to the 

 fifth grow 5mm., the fourth 4mm., while the third is the 

 slowest, growing 3.7mm. each twenty-four hours. 



Having considered the method of working, we will 

 now summarize the author's results of the progress of 

 the moult at the time when each primary is lost. 



The Young Partridge at Various Ages. 



At an age of 13 days the young bird is first 

 able to fly ; the wings are furnished with seven primaries 

 and eight secondaries, all growing. The third primary 



