the Feet of Cypselus melba. 199 



first phalanx of the three outer toes has lost its spherical 

 form and become cubical. In the ungual phalanges, in 

 which the bending towards the lower side may be seen, the 

 formation of the nail has begun. In nestlings of the 14th day 

 a fusion has commenced. Unfortunately the limbs in this 

 and in older stages, on account of their thickness, do not allow 

 of a sufficiently accurate observation of the process of fusion. 

 Sections, which I have not yet been able to prepare, would 

 probably give the desired result. Yet I believe that I may 

 safely say that in the third toe the second and third phalanges 

 fuse, in the fourth toe the metatarsal and the first phalanx, 

 and the second and third phalanx. At any rate I have 

 observed in several preparations in the upper part of the 

 second phalanx of the third toe a slight transverse groove, 

 probably the last trace of an earlier separated condition. 

 And in the fourth toe the second (that is, actually the 

 third) phalanx is in very close relation with the fourth — 

 a fusion has thus commenced. The main fact is, that origi- 

 nally the normal number of phalanges is present, if only for 

 a short time, and that they are afterwards diminished by 

 fusion. The cause of this fusion is possibly that the foot, 

 which serves to catch hold of rocks, walls, beams, &c, re- 

 quires to be strengthened, and this strengthening is pro- 

 duced by a reduction of the joints. 



A. further peculiarity of Cypselus is the short strong 

 humerus and the disproportionately long hand. In the full- 

 grown wing the length of the hand to that of the arm is as 

 7:5. This remarkable condition is only found in Cypselus 

 and iu the Trochilidee. It is interesting to find that this con- 

 dition is only the result of secondary modifications. I find 

 in a series of stages the following proportions : — 



Humerus. 



8 days' embryo 1 



10 ,, „ 1 



12 „ „ 1 



W „ „ 1 



16 „ „ 1 



Newly hatched young . . 1 



Chick of three weeks .... 1 



Full-grown 1 



r :i 



