APPENDIX. 197 



We thus greatly increase our power, and assist 

 the brevity of nomenclature ; and we gain the 

 "convenience of using the second term by itself, 

 when we wish to do so, more naturally. Thus, 

 one may shortly speak of * The Sagitta ' (when 

 one is on a scientific point where ' Swift ' would 

 be indecorous !) more easily than one could 

 speak of ' The Stridula,' or ' The Velox,' if we 

 gave the bird either of those epithets. I think 

 this of Sagitta is the most descriptive one could 

 well find ; only the reader is always to recollect 

 that arrow-birds must be more heavy in the 

 head or shaft than arrow-weapons, and fly 

 more in the manner oif rifle-shot than bow-shot. 

 See Lecture II., §§ 46, ^y^ yi, in which last 

 paragraph, however, I have to correct the 

 careless statement, that in the sailing flight, 

 without stroke, of the larger falcons, their 

 weight ever acts like the string of a kite. 

 Their weight acts simpl}' as the weight of a 

 kite acts, and no otherwise. (Compare § 65.) 

 The impulsive force in sailing can be given 

 only by the tail feathers, like that of a darting 

 trout by the tail fin. I do not think any ex- 

 cuse necessary for my rejection of the name 

 which seems most to have established itself 



