384 ME. E. DEGEN ON ECDYSIS. 



In the majority of tlie specimens the growth of these coverts proceeds in a fairly 

 symmetrical manner from both wings for either of the two systems of moult. 

 It, however, happens frequently, notably in the younger birds, that while the juvenile 

 mode is prevailing still on the one wing, the other wing may have already adopted a 

 stage of the later conditions. 



Instances of perfect symmetry for the earlier stage of simultaneous development of 

 the series arc Nos. 5, 12, and 15, which are all young birds ; while a case of dualism 

 of development occurs, amongst others, in No. 13. In this latter specimen the wing of 

 the left-side is still following the early principle of simultaneous replacement ; it is 

 marked in this case by uniformity in length of all its coverts which constitute this 

 co-series ; whereas on the right side, while still repeating the early mode on the 

 proximal portion of the cubitus from the 5th covert to the 10th (including a slight 

 modification of the 8th), the mode of the first definite formation for moulting in groups 

 has taken place on its distal part for coverts 1-4. This is shown by the diminishing 

 lengths in development of these coverts in their inward numerical order. 



In reference to the modification of covert 8, as alluded to above, it is not a little 

 curious to find this covert to be the only oue in a nascent state of growth amongst 

 those from 6-10, which are all about half-grown. Herein, then, we have an early 

 indication of plainly denoting the initial point in the ultimate formation of the first 

 group, which comprises coverts 8, 9, and 10. This arrangement corresponds exactly 

 with that of the issue of the remiges and the main coverts in this place which have 

 preceded them in development. 



Illustrations of perfect conditions for the group-moulting are Nos. 3 (left side), 

 11 (both sides), 13 (right side), 16 (right side), and probably all the remainder of 

 adults in which the moult of this co-series had been positively completed at the time 

 of their reception. 



2. Inferiores. 



Metacarpo-digital Portion. — Quite distinct from the mode of renewal by means of 

 two separate sections of their dorsal congeners at a comparatively immature age, 

 the set of coverts under consideration here apparently follows the rule which 

 applies to the remiges and the main coverts of the young individual undergoing its 

 first autumn moult, viz. in the ordinal appearance of the feathers from 1-10. 



The main cause for this ajjparent ^ difference lies in the fact that they begin to moult 

 later than their companion coverts of the dorsal series ; but this is a delusion only. 

 It is not until from three to four of the latter have emerged and are fairly developed 

 that the first ventral median begins to replace its old feather. The others follow suit 

 in rapid succession, completing the inner section with the 6th, and so reach the 7th 

 covert or first of the outer section at about the same time as this latter emerges from 

 the skin. This arrangement gives it the appearance of a continuous growth for the 

 whole series, and therefore produces the delusion referred to before. 



