134 Degeneration in the Ostrich 



ostrich the experimental confirmation of the issues involved is scarcely 

 possible. About three years intervene between the beginning of one 

 generation and the next ; moreover all the birds are of mixed ancestry, 

 sufficient time having not yet elapsed to build up strains which are 

 " pure " as regards any one of the variable characters. 



While still a matter on which geneticists are by no means agreed, 

 and in the absence of experimental proof, it is held that the gradual 

 diminution in size of a structure in a degenerative phase is most feasibly 

 explained as evidence of a slow degradation on the part of the germinal 

 factors concerned '. The weakening is probably to be interpreted as the 

 result of successive factorial losses, perhaps following upon fractionation, 

 the expressive power of each loss being so small that the appearance of 

 continuity is preserved. The " multiple allelomorphs " of Prof Morgan 

 indicate that a single unit factor may exist in a great number of grades, 

 while the " multiple modifying factors " suggest that a visible character 

 may be modified in the finest gradations by alterations in different parts 

 of the germinal apparatus. These would appear to render unnecessary 

 an appeal to a direct change in a factor itself Prof W. Bateson in his 

 Presidential Address before the British Association in Australia in 1914 

 is however " satisfied that they may occasionally undergo a quantitative 

 disintegration, with the consequence that varieties are produced inter- 

 mediate between the integral varieties from which they were derived." 



Where a retrogressive mutation shows Mendelian dominance the 

 presence of a factorial influence of an inhibitory nature would seem to be 

 justified ; or it may be that a factor for a somatic loss is dominant over 

 one for its presence. Where Mendelian recessiveness is obviously not 

 involved, and having regard to the general retrogression in progress, the 

 disappearance of a structure is deemed to correspond with factorial loss, 

 or possibly of degradation to such a degree that it is incapable of gaining 

 somatic expression. 



Reference is sometimes made to the supposed greater variability of 

 domesticated animals as compared with wild animals. The conditions 

 in the ostrich are clear on this point. Though all the examples studied 



^ As modifying a simple attitude of this kind Prof. Morgan [I.e. p. 50) writes : "The 

 hypothetical situation is, however, uncertain in a high degree the moment one realizes 

 that changes up and down of a character appear more often brought about now by one, now 

 by another gene, rather than of the principal one, i.e. the one on which, owing to a 

 mutation, especial attention is focussed." And again, referring to palaeontologists as 

 advocates of orthogenesis or continuous variation with a definite trend : "They overlook 

 the fact that to-day there is experimental evidence demonstrating that variations as small 

 even as those they record have been shown to rest on mutational changes." ^ 



