THE HUMMING BIRDS. 



299 



Ordiuarily, there is a regular gradation iu the size aiid shape from 

 the first to the tenth primary ; but sometimes this is not the case, the 



Fig. 21. — Wing of Trochilus colubris, adult male. 



male of the common Ruby-throated Humming Bird (Trochilus colubris) 

 affording a conspicuous example. In this, the six innermost quills are 



Fig. 22. —Wing of Sphenoproctus pampa, to show excessively thickened shafts of three outer primaries. 



not only abruptly much smaller than the others, but they are quite 

 differently shaped at their tips (see Fig. 21). 



Fig. 23.— Wing of Eupetomena macroura. 



Although the shafts of the primaries are always hard and strong, to 

 enable them to endure the rapid vibrations to which they are subjected 

 during flight, they are not often conspicuous for their unusual thick- 



Fig. 24. — Wing of Aphantochroa drrhoehloris. 



ness. In some genera, however, they are thus extraordinarily devel- 

 oped, in Sphenoproctus and some species of Campy lopter us, for example, 

 appearing almost like a monstrosity or abnormal swelliug, as shown 



Fig. 25.— Outer primary of a species of Campy lopterus, showing thickened shaft. 



in (Figs. 22 and 25), which is accompanied by others (Figs. 23 and 24) 

 to show the gradual transition through which this excessive develop- 

 ment is reached. 



