Anatomy &c. of the Colies. 249 
plate perforated by a single foramen. The shaft is flattened 
antero-posteriorly, and has the outer border produced into a 
sharp edge, which, as it approaches the hypotarsus, widens 
out into a thin flange pierced by a small fenestra. 
V. SumMMARY. 
It must be evident, to those who have read the earlier 
sections of this paper, that the question of the systematic 
position of the Colies is not one that can be easily or over- 
confidently answered. But all the available evidence tends 
to shew that the nearest allies of this group are the Cypseli ; 
though, as will be seen, in many points the two groups do 
not agree very closely, and this more especially with regard 
to the skeleton. 
In the matter of their pterylosis the Colit and Cypselt 
shew a remarkable and significant likeness, and this is most 
apparent, perhaps, when nestlings are compared. In the | 
present paper these comparisons have been made between 
Colius affinis and Cypselus apus. 
In both groups the pleryla capitis is interrupted by an 
apterion; but while this apterion in Colius is of considerable 
size, and extends outwards to join the ocular area behind 
the eye, in Cypselus apus (for example) it is very narrow 
and joins the ocular area in front of the eye. Moreover, the 
feathers are arranged differently in the two types. In 
Cypselus apus there is a sharply defined, tongue-shaped, 
frontal area, wherein the feathers are closely set, contrasting 
with the more sparsely feathered parietal area. 
In both the Colii and Cypseli the spinal tract is interrupted 
by a long narrow apterion, while the pteryle are of unusual 
width throughout the body, thus reducing the apteria to a 
minimum. ‘The difference in the form of the wing is entirely 
due to the difference in habit between the two groups, the 
one being of a sedentary habit and flying little, the other 
extremely active and depending for sustenance on insects 
caught in mid-air. 
The myology of the two groups, when compared in this 
connexion, is less convincing. A comparison of the wing- 
