192 Degeneration in the Ostrich 



Such diverse factorial possibilities for an apparently simple process 

 as a continuous reduction in size of a claw serve to reveal that until 

 experimental mutation can be reduced to simpler terms its results can 

 hardly be used as an instrument for procuring a clear conception as to 

 the factorial changes involved in evolutionary processes generally, and 

 the evolutionist may have to remain content with the somatic expression 

 of his characters by whatever germinal process they may have come to 

 be. The evolutionist would naturally desire to bring his facts into 

 harmony with Mendelian results, and adopt their interpretation, but 

 when any simple change may apparently be due to any one of such a 

 multiplicity of germinal agencies, any assurance of correctness can only 

 be gained through separate studies of the magnitude of those already 

 carried out by Morgan, Castle and others. The recent paper by Prof 

 Morgan, " Evolution by Mutation," full as it is of warnings as to the 

 dangers of interpreting somatic changes in factorial terms, is sufficient 

 commentary. Probably Morgan is quite justified in his remarks "It is 

 true that when writers have brought forward evidence of continued and 

 progressive change in a character they have not concerned themselves 

 with the analysis of the change in the germ plasm that has brought it 

 about — in fact, in most of these cases the possibility of advance in a 

 principal gene or of advance through modifying genes had not been 

 appreciated or even understood." But when one thinks of how many 

 years of intensive work it has taken to arrive at some of the conclusions, 

 and with material peculiarly well adapted to the purpose, it is small 

 wonder that students of evolution have not been able to do the same. 

 Perhaps it may be replied that it is only the evolution of the germ plasm 

 which counts, that of the soma being merely a product of the germ, and 

 of secondary import. For in the end, evolution is determined by the 

 germ plasm rather than by the soma. 



The remarkable variation between the right and left sides of bilateral 

 structures which are in a degenerative phase would appear to be of some 

 significance. All the degenerating structures of the ostrich display it — 

 plumes, scales and claws ; the limit of variation being approximately that 

 of the degenerating element or elements for the time being. Thus 

 among the plumes a difference of only one or two is displayed by the two 

 wings, and in any row usually only one or two of the end members are 

 in a degenerative phase ; a vestigial claw may be present on the toe on 

 one side and not on the other. If in the same individual an asymmetry 

 of this nature is possible between the two sides produced from the same 

 zygote it engenders reflections as to the uncertainty of the facts of varia- 



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