BLASTOGENIC VAEIATIONS. 113 



to abolish the normal resistance to cross-fertilisa- 

 tion. If differences of nutrition in the parental germ- 

 plasms as a whole can produce such profound effects on 

 the offspring to which they give rise, then, supposing it 

 is possible that various individual portions of the germ- 

 plasm are capable of being more or less independently 

 affected by inequalities of nutrition, there seems no rea- 

 son to doubt that they may show a similar reaction, and 

 so give rise to variations in the individual parts of an 

 organism which they represent or " determine." 



Experiments upon higher organisms are, of course, 

 very much more difficult to carry out than those upon 

 sea-urchin larvae, but nevertheless Professor Ewart * 

 has been able to bring to a successful conclusion some 

 experiments upon rabbits. Thus he found " that if a 

 well-matured rabbit doe is prematurely (i. e., some time 

 before ovulation is due) fertilised by a buck of a differ- 

 ent strain, the young take after the sire; when the fer- 

 tilisation takes place at the usual time, some of the 

 young resemble the buck, some the doe, whilst some 

 present new characters or reproduce, more or less accu- 

 rately, one or more of the ancestors. When, however, 

 the mating is delayed for about thirty hours beyond the 

 normal time, all the young, as a rule, resemble the doe. 

 It may hence be inferred that in mammals, as in 

 echinoderms, the characters of the offspring are related 

 to the condition of the germ-cells at the moment of 

 conjugation, the offspring resulting from the union of 

 equally ripe germ-cells differing from the offspring de- 

 veloped from the conjugation of ripe and unripe germ- 



* Presidential Address before the British Association. Vide Na- 

 ture, vol. hdv, p. 482, 1901. 



