J. E. DUERDEN 185 



are all convincing testimony of some consistent force, to all appearances 

 acting apart from any environmental influence. They are beyond the 

 ordinary germinal variations which a mixed assemblage of individuals 

 of a species presents. It was evidence of this nature, but in a pro- 

 gressive direction, that led Nageli to think of a mystical, internal, 

 vitalistic force as directing organisms, and others to postulate an " inner 

 directive force," an " inner law of development," or an "intrinsic tendency 

 towards progress " ; and in the degenerative phenomena of the ostrich 

 we seem confronted with facts similar to those for which these phases 

 stand, to-day regarded with so much suspicion. Morgan (^.c, p. 50) 

 remarks : " an orthogenetic series of changes does not in itself, without 

 a closer analysis than has as yet been furnished, establish that an innate 

 principle, urge, vis-a-tergo, or driving 'force' is causing the successive 

 moves. The genetic evidence from multiple factors must create at least 

 a strong suspicion against the ' will to believe ' in the mystic senti- 

 ments for which these terms always stand. That a progressive series of 

 advances in a gene might take place with a consequent advance in the 

 many characters involved is thinkable, especially if it could be shown that 

 environmental changes cause parallel progress in the gene and this in 

 the character." 



It may be suggested that instead of being due to some mystical, 

 vitalistic, directing force the changes in the ostrich are to be interpreted 

 in terms of germinal senescence, perhaps expressing itself in factorial 

 fractionation and loss. It is averse from all our experience of nature to 

 think of anything as fixed and immutable, and much more is this the 

 case when considering organic matter, the most unstable of all. We are 

 schooled in the senescence of protozoan and somatic cells, but the long 

 contemplation of the phrase, "immortality of the germ plasm," has 

 tended to divorce our ideas of the germ-plasm and somato-plasm, as 

 though they were two distinct kinds of proto-plasm wholly apart. Just 

 as there have been periods of " momentum in evolution," when certain 

 groups progressed even to bizarre degrees, presumably as a resull of 

 germinal virility and exaggerated factorial change, so there have been 

 periods when groups have been retrogressive and decadent, expressive 

 of factorial degeneracy. The ostrich and the entire group to which it 

 belongs, the Ratitae, may be deemed to be one of these at the present 

 time ; in this respect they represent probably the most striking group 

 of degenerate vertebrates which could be adduced. Parts of the germ 

 plasm at least must be common to the entire sub-class, and may well 

 be subject to the same senile changes. 



