938 SUMMARY OF CURRENT RESEARCHES RELATING TO 



feathers. In his investigations young chicks and ducklings within 

 the egg (from the sixth to the tenth day) were treated for a few 

 minutes with a concentrated solution of corrosive sublimate at 50° C, 

 and were then washed with dilute alcohol. Relative portions were 

 hardened in alcohol and stained with picro-carmine. The same 

 method was applied in the study of feather regeneration. 



The first feathers or dunes are briefly discussed in their primitive 

 form and then in their development. The extension of the growing 

 epidermis is referred to in explanation of the origin of the folds 

 which give rise to feathers and similar structures. Into the papilla 

 formed from the thin outer " epitrichium " and the mucous layer, a 

 nourishing cutis papilla penetrates, richly furnished with capillary 

 branches. A number of clefts appear in the epidermis, and between 

 these elongated cells of the cutis insinuate themselves, from the apex 

 downwards. These clefts mark off the principal rays of the future 

 dune, and the epidermic material enclosed between each two clefts 

 serves for the construction of each medulla-containing ray. While 

 this stellate notching is progressing, the papilla is still growing in 

 length. In consequence of the insinuation of the cutis within the 

 clefts, the outer epidermal cells come into more nutritive relations 

 and become cylindrical like those of the mucous layer. A capillary 

 lies in each corner of the stellate figure. The cylindrical cells at 

 each side of the cleft begin to extend peripherally, and become 

 cornified ; the round cells which they enclose as in a tube, form the 

 central medullary cells. The more peripheral round cells which are 

 not included go to form the secondary rays associated with the above- 

 mentioned tubes or principals. The cylindrical cells also share in 

 forming the basal portions of the secondaries. Meanwhile the cutis 

 papilla is dying. The basal piece of the feather is the undivided 

 root of the papilla. The " epitrichium " is loosened during the 

 folding or notching, rapidly becomes horny, and is, as is well known, 

 thrown off when the young bird leaves the egg. A considerable 

 number of different forms of dunes are then described. 



After describing briefly the familiar structure of the adult feather, 

 and noting especially how the superior margin of each radius is folded 

 so as to form a perfect groove in which the hamuli of the anterior 

 radius lie, Dr. Klee passes to discuss the development. Even within 

 the egg the apex of the future feather appears at the base of the 

 dunes. The whole papilla sinks deeply in the skin. The capillaries 

 multiply in number, more than a hundred being often present. The 

 number of epidermic layers is also very considerable. More numer- 

 ous clefts arise as before, the corium insinuates itself, round cells 

 become cylindrical. Two associated rows of the latter enclose, as 

 before, a number of round cells, forming the future medulla. The 

 majority, however, do not form these rami, but retaining their dis- 

 position in two rows form the radii. The cylindrical cells composing 

 each row stretch peripherally, and becoming bent form the cilia or 

 hamuli. 



The development of the shaft and after-shaft, the nature of the 

 calamus, and the modifications of the cutis papilla are then discussed. 



