182 Deg enteral ion hi the Ostrich 



generation, until final atrophy is reached. Thus the germ plasm of the 

 ostrich may contain numbers of factors at various stages of degradation 

 without any manifestation of them in the soma. The germ of an 

 organism in a degenerative phase may be a very different matter from 

 the evidence we have of its nature in the soma. 



The factors concerned with the lost digits of the wings and legs are 

 not yet entirely lost to the germ plasm of the race or of the individual, 

 but only fail to continue their manifestation to a late ontogenetic period. 

 As already shown traces of at least four digits occur in the wing after 

 about ten days' incubation. The metacarpal of the fourth has but a 

 brief persistence ; the second and third are for a time co-equal in their 

 expression, but the latter never completes its development and varies 

 much with regard to the second phalanx. Traces of the five digits or 

 their metatarsals occur in the foot of the ten days' chick. The first and 

 fifth have a very transient ontogenetic existence, the second remains 

 much longer, while only the third and fourth continue as digits through- 

 out the life of the bird. 



Although we assert that the ostrich has only three digits to the wing 

 and two to the foot the remark should be accorded a time qualification. 

 At a certain stage in its ontogeny the bird has hints of four and five 

 digits respectively. Expressed factorially we should say that the genetic 

 factors for the digits are present in the zygote ; some gain somatic 

 expression for only a brief, transient ontogenetic period and others per- 

 sist for the life-time of the bird. For the former we may hold that some 

 ontogenetic weakening or inhibition takes place and they cease to be 

 effective beyond a certain stage, but the factors have by no means 

 wholly disappeared from the germ, as in the losses of the remiges and 

 coverts. 



The persistence of factors only in the embryo stage, but presumed to 

 have been effective throughout the ancestral phylogeny and in a form 

 resembling other living types, is manifestly the Mendelian manner of 

 expression for the principles represented by the Biogenetic Law of von 

 Baer and the Theory of Recapitulation of Haeckel — the individual in 

 the course of its development passes through stages corresponding with 

 its course of evolution ; ontogeny repeats phylogeny. This means that 

 the factor or factors for a structure now degenerate still persist in the 

 germ plasm, but in a degraded form, so reduced that they find expression 

 for only a short period in the early stages of ontogeny ; or perhaps the 

 factors which represented the later ancestral feature have completely 

 degenerated, and only the earlier ones persist. There is not a throwing 



