MUTATIONS AND EVOLUTION. 315 



All the mutative changes appear to be wholly intrinsic in 

 their origin and independent of any environmental influence ; the 

 characters resulting are deemed to have no adaptive or welfare 

 value, beyond these of a purely incidental and temporary nature; 

 natural selection is held to have no directive influence, but will be 

 eliminative when retrogression has proceeded so far as to fnterfere 

 with the necessary activities of the bird. 



INHERITANCE OF CALLOSITIES IN THE OSTRICH. 



Bv Prof. J. E. Duerdex. M.Sc. Ph.D. 



(Abstract.) 

 Read July 10, 1919. 



Apart from the strong callosities on its feet and ankles, the 

 ostrich has two conspicuous, thickened pads over the parts of 

 the body upon which it rests when crouching, namely, one over 

 the rounded projecting sternum in front and another over the 

 pubic symphysis behind. They present the appearance of hard, 

 rough thickenings of the skin, manifestly formed as adaptations 

 to the pressure and friction to which the two projections are 

 subject when the bird crouches on the ground or rolls from side to 

 side. They afford a strong contrast to the surrounding smooth 

 skin, and there is no question that they could be formed naturally 

 as a result of the habits and activities of the bird, in the same 

 manner as callous thickenings are developed on the human hand 

 as a result of manual labour. 



It is found, however, that the callosities occur over the 

 sternum and pubis of the ostrich chick prior to hatching, and 

 are consequently to be regarded as hereditary structures. We 

 have, therefore, a hereditary character of a form and nature 

 exactly sirnilar to one which Avould otherwise be acquired 

 independently from the known habits of the ostrich and the 

 established responsive nature of its skin. The same structure 

 has a germinal origin, and could also be produced in the course 

 of the life-time. It is hardly conceivable that a change could 

 have occurred independently in the germ plasm of such a nature 

 as to give rise to a somatic character, having exactly the same 

 nature and situated in the same ])lace as one which would be 

 naturally produced from the activities of the organisms, and it is 

 contended. that the chick callosities can only be interpreted as 

 instances of acquired characters which have in some manner 

 become transmissible. Natural selection can have no guiding 

 influence, for, even if not transmissible, the thickenings would 

 arise as needed, just as they do on the human hands. 



