THE MUTATION THEORY AND MUTATIONS. 175 



De Vries holds that mutation is directionless. How does it happen that the 

 same set of mutations continually recur year after year in a succession of genera- 

 tions from a single stock, and likewise from different stocks or families? 



This is conclusive that the character of the mutation is nothing accidental; the 

 mutations are not one thing in one plant, another thing in another plant, one thing 

 this year, another next. They are the same kinds repeated, some with more, some 

 with less, frequency in each sowing. 



The doctrine of multifarious mutation has to be saved by an assumption that 

 has no foundation in observation, namely, that mutation started originally in a 

 haphazard direction; but it was then passed on as a "latent" thing by heredity. 

 It is, then, founded on a pre-existing, definite basis every time, except the time 

 when it first made its appearance as an internal character. This is a premutation — 

 actual mutations are all preceded by latent ones appearing in a premutation period. 



If white dots, formed in the same way, in Geopelia cuneata and in a rail are a 

 mutation, then mutation follows in one way rather than many ways. The same 

 mutation occurs in different species. Spots appear in homologous places and accord- 

 ing to the same law. These facts tell against an "orderless" mutation. 



De Vries holds that species are separated by absolute gaps that can not be 

 closed up. They arise by jumps or as sports. Were this the case we ought to see 

 sudden gaps in fertility. I find that fertility is a thing of degrees — i.e., it is at an 

 optimum within the species, but it diminishes gradually, not by steps, as we pass 

 from the crosses between species closely related to crosses of species wide apart. 47 



Again, fertilization within the species is of every degree, and results therefore 

 in simple penetration of sperm which fails to make more than an early beginning 

 of development or nothing at all, or it may give stages of change, etc., up to blood 

 formation, and from this point it may go on and stop after forming an embryo, or 

 at any point up to hatching; and when hatched, the fate is not yet settled; the bird 

 may be deformed and still live; it may be too weak to develop further or go on and 

 die at 3, 4, 5, 6, or more days. 48 All along the line we see that development requires 

 energy and stops or goes wrong for failure in this. 49 



We have to remember that all permanent modifications in species have to be 

 represented in the germs. Further, that " continuity of germ-plasm" is the funda- 

 mental fact in heredity. There is really no transmission of characters anywhere 

 in the organic world. There is growth by assimilation and self-division, but no 

 transference of characters from parent to offspring. Parent and offspring are each 

 independent developments, alike or different according as the germs from which 

 they develop are alike or different, and according as the conditions of development 

 and life are alike or different. 



All organic likeness depends on assimilation — the physical process of intussus- 

 ceptional growth — akin to crystallization. In the crystal we have stable equi- 



47 Examples of such a series are the following: White and blond ring; Japanese ring and blond ring; blond ring 



and Chinese ring; blond ring and European turtle, blond ring and tiger turtle; blond ring and 1 ler. And similar 



to the last named, blond ring and Eelopistes; white or blond ring and mourning-dove; blond ring and white-wing; 

 common pigeon and Japanese turtle. (These five last-named crosses are all of family or of subfamily rank. -Ed. ' 



48 Young birds often make failures. Doves reach the highest point at 3 to 4 years. 



49 The energy of development and degree of fertility appear to be correlated. May the same developmental process 

 run to different lengths, according to the greater or less strength or energy? 1 think the male in many species of birds 

 passes directly through and beyond the female stage. In many cases even I he females may now and then pass beyond 

 the normal female and advance towards the male condition. Ontogenies seem to lengthen, if the biogenetic law is true. 

 and perhaps all evolution depends as much on lengthening as on modification. 



