1883.] 235 [Jeffries. 



Of the homology of the claws in the group of birds there can 

 be no doubt ; that the claws of birds are homologous with those 

 of reptiles and mammals is also apparent. Their relations to other 

 appendages have been variously stated, comparisons to scales and 

 " agglutinated hairs " having been made. There is, however, no 

 similarity to either ; a claw is simply a horny coat of the end of a 

 digit. Claws have a decided histological resemblance to the 

 beak, nothing more. So claws must be regarded as devoid of 

 morphological relations to other epidermal structures. To follow 

 out the definitions given in this article, claws, if on the same 

 digit, are morphologous structures ; if on different digits homol- 

 gous structures. 



Passing from the claws we come to the scuta. These have 

 been assumed " a priori " by many authors to be morphological 

 with the scales of reptiles ; a proceeding totally unscientific. Not 

 only this, but feathers, scales and hairs have been said to be the 

 same thing ! There are three ways by which we may follow 

 morphological relations : by comparison and formation of series 

 in adults, by palaeontological successions, and by similarity in 

 development. In each case care must be taken to guard against 

 mistaking resemblances due to general physiological laws for 

 resemblances due to genetic connection, and confounding anal- 

 ogous with morphologous structures. 



The evidence in favor of the idea that scuta are scales may 

 be set down as follows : first, both look more or less alike and 

 have similar functions, *. <?., those of protection and ornamenta- 

 tion ; secondly, they are both essentially flaps or folds of both 

 layers of the skin, pointing to the posterior end, and arranged in 

 quincunx order, and to the superficial glance seem to form a fair 

 series ; lastly, the first stage of their development is much the 

 same, the same layers of the epiderm being distinguishable in 

 each. No other evidence, so far as I know, exists. 



On the other hand the evidence against the morphology of 

 scuta and scales is overwhelming, and the foundation of the 

 three preceeding arguments rests on an unsubstantial basis. The 

 first is of no value as evidence, and is only the foundation for 

 fallacious a priori conclusions. The second has but little more 

 worth. Reptilian scales have invariably a certain number of 

 epidermal layers which in birds are only to be found in the em- 



