that connect the Orders and Families of Birds. 429 



Merops becoming shorter as they approach Hirundo ; while those 

 of some of the latter group partially desert their own type, and 

 by degrees assume the lengthened form of the bill of the Bee- 

 Eaters. The tail of Merops, again, is equally found to desert the 

 typical character of the group, namely, the greater length of the 

 two middle feathers, in order to become even in some species, 

 then slightly forked, and at length to be identified with the fully- 

 forked tail of Hirundo. 



In continuing to trace out the same line of affinities between 

 the succeeding groups, it is unnecessary to enter into a detail of 

 those characters which unite the two families of Caprimidgida 

 and Hirundinida. The union between them in the most essen- 

 tial particulars, in their habits, economy, and general conforma- 

 tion, is too evident to the common observer, and too universally 

 acknowledged by scientific writers, to need any further illustra- 

 tion. It is gratifying, however, to observe, how even in mi- 

 nute particulars a gradual succession of affinities imperceptibly 

 smooths the passage between conterminous groups ; and I can- 

 not pass over without remark, the circumstance of the hind toe of 

 Caprimulgus being usually retractile, which enables it to place all 

 its toes in front, in a similar position to that which they maintain 

 in Cypselus, where the family of the Hirundinidce terminates. The 

 conformation of the tail in the two families shows a similar affi- 

 nity. Some species of Caprimulgus lately arrived from Brazil, 

 exhibit the forked tail of Hirundo, one of which indeed, the 

 C. psalurus of M. Temminck, has this character developed to an 

 almost disproportionate degree. 



Leaving those typical families with the short bill, and taking a 

 general survey of the tribe, we may perceive that the Caprimul- 

 gidcB unite themselves to the longer-billed families by means of 

 the Linnean Todi, which preserve the broad base of the bill of the 

 latter, but lead on by the comparative length of that member to 

 the succeeding family of Halcyonida. If we compare the bill of 



3 K 2 the 



