IXXX GENERAL INTRODUCTION. 



to other embryos by a different sire. But even should 

 further experiments justify this conclusion, it does not 

 follow that there is either telegony or saturation."^ 



I have been led to refer to saturation because the 

 second hybrid of the Clydesdale mai-e is more a zebra 

 than her first. Some seem to think the Clydesdale has 

 already been ''saturated ^' by the zebra. It is a matter 

 of common knowledge that the members of any given 

 family, litter, or brood by the same parents vary con- 

 siderably in coloration, form, and disposition. That the 

 second Clydesdale hybrid differs from the first is hence 

 not a unique, nor yet an unexpected phenomenon. But 

 though the members of the same family often differ from 

 each other, it by no means follows that the cause of this 

 variation has yet been discovered. 



If the dam in form, &c., gradually assumed the cha- 

 racters of the sire, and if the resemblance of the offspring 

 to the sire proceeded at a progressive rate, there would 

 be a presumption in favour of saturation. But un- 

 doubtedly this is not invariably the case, and when it 

 does happen that the female appears to assume the cha- 

 racters of her mate, or the offspring to become more and 

 more like their sire, a simpler, or at least a more scientific 

 explanation will doubtless be available. In lai'ge families 

 the youngest children often take more after the mother 

 than the eldest. Of Lady Meux's three hybrids out of 

 the same zebra mare, the youngest is undoubtedly most 

 like a horse, but the intermediate one is by a long way 

 most like a zebra. The Clydesdale's second hybrid is far 

 more a zebra than her first, not in colour, but in make 

 and gait and disposition. If the striking difference be- 

 tween the two full sisters is not due to saturation, how 

 can it be explained ? A possible explanation will be 

 easier if we consider for a moment some of the results of 

 cross-fertilisation. It is almost inconceivable that two 

 germ-cells derived from two separate animals or plants 

 can ever be identical either in form or structure. Hence, 



* Experiments with toxins might prove that pliysiological " infection " 

 occurs. 



