Pterylography of the Houtzin. 363 



(fig. 3j p. 361), and the domestic Turkey, I find that remiges 

 1-7 have attained a considerable degree of development, 

 while the three distal remiges are as yet only represented by 

 neossoptiles ; thus, as in Opisthncomus, a free finger-tip is 

 left. The exchange, however, of a terrestrial for an arboreal 

 habit has brought about an exaggeration of one feature whilst 

 it is eliminating others, inasmuch as an accelerated develop- 

 ment of the metaearpo-digital remiges has plainly taken 

 place, whilst the once long hand is being gradually shortened ; 

 the manus, however, is still (11) 'Monger than the forearm, 

 .... but the 2nd digit is scarcely produced beyond the 

 wing-membrane, and the claw has been lost, though present 

 in the embryo, the pollex has retained the claw and extends 

 just up to the 3rd digit.''' 



The accelerated development of the metaearpo-digital 

 remiges, just referred to, can best be understood by a com- 

 parison of fig. 3, p. 361, i-epresenting the wing of a nestling 

 Fowl, with that of Opisthocomus (stage 5), PI. XI. fig. 3. A 

 glance will serve to show that while in Opisthocomus all the 

 remiges are represented by definitive feathers, and whilst there 

 is a perfectly easy gradation in the length of the same from 

 within outwards, the terminal feather being the smallest of 

 the series, in that of the Fowl there is an abrupt change 

 from definitive feathers to neossoptiles, the change taking 

 place directly after the 7th remex. 



It seems probable that these remiges have undergone what 

 we might describe as a process of forcing — or, as I have 

 already called it, accelerated development — in which the 

 proximal remiges have developed at an excessively rapid 

 rate, so as to out-distance their fellows at the distal extremity 

 of the wing, which are as yet only represented by neosso- 

 ptiles. The rapid development of these seven remiges is pro- 

 bably due to the fact that the terrestrial mode of life demanded 

 the aid of the wings for the purposes of flight at an earlier 

 period than would be the case if they still dwelt, like 

 Opisthocomus, in comparative security amongst the trees. 

 According to this theory the function of the claw of digit ii. 

 begins to wane as soon as the distal remiges project beyond 



