3l6 INHERITANCE OF CALLOSITIES IN THE OSTRICH. 



In support of such a heterodox view, it is submitted that a 

 character may become transmissible without necessarily being 

 germinal, in the sense of having factorial representation in the 

 germ plasm. Acquired characters are somatic modifications 

 which are produced as responses of the organs and tissues to 

 stimuli from the environment or from use and disuse, and reveal 

 an inherent power of resjx)nsive adaptability in organisms. It is 

 suggested that where responses are continued generation after 

 generation, as in the case cf the callosities of the ostrich, they 

 may, as a result of the structural inter-relationships established, 

 gradually appear earlier and earlier in the ontogeny of the 

 individual and independently of the primary stimuli, and in 

 time come to be formed prior to hatching. They may become 

 transmissible characters without necessarily being germinal, that 

 is, without having distinct factorial representation. 



On a hypothetical conception of this kind, it may be under- 

 stood that the continued production of sternal and pubic callosities 

 has introduced such fixed and intimate inter-relationships of the 

 structural parts concerned that in the end they come to replace 

 the old inter-relationships altogether, and with them the non- 

 callous state. The callosities are formed antecedent to and apart 

 from the primary stimuli. Their appearance becomes accelerated, 

 as it were, and they arise even before the chick is hatched and 

 the original stimuli can be eflfective. They are not new charac- 

 ters which have come in, but are new as regards the ontogenetic 

 time at which they appear. 



While the body of the crouching ostrich is mainly supported 

 upon the median sternal and pubic callosities, it is steadied 

 laterally by the ankles and feet, and these shew strong thickened 

 pads which are also hereditary. Usually, however, an accessory 

 pad forms on the inner side of that at the ankle, and the bird rests 

 upon this acquired thickening instead of upon the hereditary one. 

 Manifestly some modification in the crouching habit of the ostrich 

 has taken place, since it no longer uses its hereditary ankle 

 callosity, but forms a new one. It is suggested that the original 

 callosity was functional when the ostrich was at the three-toed 

 stage of its evolutionary history, and that since the degeneration 

 of the inner (second) toe a new support has become necessary 

 on mechanical grounds. The original callosity is hereditary and 

 non-functional, while a new functional callosity takes its place, but 

 is non-hereditable. 



