1916] Chandler: Structure of Feathers 305 



ture as compared to those of the species already described. The 

 distal barbules for the greater length of the barbs have well-formed 

 bases with no flexules, only two or three weak booklets, and no 

 dorsal cilia. The proximals, at the base of the feather, have only 

 two small, inconspicuous ventral teeth, but acquire four long and 

 slightly wavy ones farther distad on the barb. Near the tip of 

 the barbs the flexules are developed, beginning nearest the pen- 

 nulum instead of at the proximal end of the base, the latter be- 

 coming narrow and reduced, concomitant with the development of 

 the flexules. This is well shown in plate 17, figures 12a and 6. 



In Pelecanoides urinatrix, belonging to the genus which may be 

 regarded as the least specialized member of the group, the breast 

 feathers have the barbules for the greater part of the barb weak, 

 but of ordinary type, i. e., without flexules. The bases of the 

 distals are narrow and elongate, the ventral tooth, usually single, 

 very small and simple, and the pennula hardly longer than the 

 base, slender, with usually only two weak booklets ; a series of 

 short ventral cilia similar to those of the body feathers of loons 

 (pi. 16, fig. 8e). The proximals do not possess the elongate, wavy 

 ventral teeth so characteristic of the more specialized members of 

 this order, but have these structures so small and inconspicuous 

 as hardly to be discernible at all. Near the tip of the barbs the 

 same sort of a change takes place that occurs in Oceanodroma, i. e., 

 a development of fiexules with an accompanying reduction of the 

 base, the ventral cilia being still well developed. The similarity 

 of this type of barbule to those developed at the tip of the barbs 

 of the breast feathers of loons seems highly significant. This re- 

 semblance is strongly brought out by a comparison of p]ate 17, 

 figure 125, with plate 16, figure 8/, representing the barbules of 

 the tip of barbs of breast feathers of Oceanodroma and of Gavia 

 respectively. 



c) Down 



The down barbules in Diomedea and Puffinus (pi. 34, fig. 97) 

 are characterized by rather long, forward-curving prongs which are 

 slender and cilia-like in form, sometimes nearly 0.04 mm. long and 

 not infrequently forked. They are longest near the base of the 

 barbule, decreasing to rudimentary prongs toward the tip. The total 

 length of the barbules sometimes reaches 1 mm., but is usually some- 

 what less. 



