1916] Chandler: Structure of Feathers 313 



middle portion of the barbs. The pennula are short, not over half 

 the length of the bases. In no birds which I have examined is 

 there a greater difference between the length of the bases of distal 

 and proximal barbules on the same barb. To counterbalance this 

 great difference in size, in order to produce fairly equivalent 

 vanules, the angle of insertion of the distals is unusually wide, 

 while that of the proximals is unusually acute, this in turn result- 

 ing in an astonishing difference in number of barbules per unit of 

 measure. While there are 40 or more distals per millimeter, there 

 are only 16 or 17 proximals for the same distance. 



On the outer vane the distal barbules differ from those of the 

 inner vane only in the absence of the dorsal cilia, and sometimes in 

 the presence of one more booklet. The proximals (pi. 19, fig. 17c), 

 except on a small portion of the tip of the barb, are similar 

 to those of the inner vane except that they are short, and rela- 

 tively broader. On the distal part of the barb the ventral teeth 

 increase to about six in number, become separated, and are trans- 

 formed into very long, stout, curved barbicels, resembling the teeth 

 of a large-toothed comb. The pennulum is shortened so that it 

 does not extend more than one cell beyond the barbicels ; the base 

 is likewise shortened and reduced. 



The primaries of Pelecanus californicus are similar to those 

 described above. The secondaries and coverts, however, have the 

 distals transformed to produce the characteristic hoary effect. 

 These barbules (pi. 19, fig. 18a) have their bases reduced in size, 

 the booklets shortened, and the pennula elongated, with a double 

 series of long, slender cilia. They resemble very closely the distal 

 barbules of the hoary feathers of Phalacocorax (pi. 18, fig. 14e), 

 but the pennula are not so broad, while the cilia are longer and 

 more prominent. 



In the breast feathers of Pelecanus, at the base of the barbs 

 the barbules have a structure similar to that found in Sula and other 

 Steganopodes, a proximal barbule from this portion being shown 

 in plate 19, figure lie. The outer portion of the barb, however, 

 develops typical flexules on both distal and proximal barbules, ex- 

 actly as in the Procellariiformes. Plate 19, figure lid, shows a 

 distal barbule from a breast feather of P. erythrorhynchus and 

 comparison with plate 17, figure lOe {Diomedea exsulans) will 

 show the striking similarity. At the extreme tip both barbules 

 assume the form shown in plate 19, figure 19e (Phaethon), which 



