Ixxxiv GENERAL INTRODUCTION. 



Taking all the facts into consideration, instead of 

 ascribing the difference between the first and second 

 Clydesdale liybrids-to saturation, I am inclined to ascribe it 

 partly to more pronounced reversion, but mainly to better 

 nutrition — to a greater ripeness — of the germ-cells from 

 wliicli it originated. 



In the same way I account for the difference between 

 members of the same family, and between full brothers 

 and sisters of the same litter or brood. Sometimes the 

 difference is due to abnormal or discontinuous variation — 

 to some of them being sports, — sometimes to more or less 

 marked reversion to the ancestors of either parent, but in 

 the majority of cases I believe it is mainly a question of 

 nutrition.* The experiments with Echinoderms f already 

 mentioned especially suggest this. Whether the hybrid 

 Echinodertiis resembled the one species or the other 

 depended on the relative degree of ripeness of the germ- 

 cells. At the beginning of the season, when the germ- 

 cells of the one species (Species A) were unripe, the hybrids 

 resembled the other species (Species B) ; but as ripe germ- 

 cells of Species A increased, the hybrids became more and 

 more like A. It is equivalent to saying the prepotency of 

 the germ-cell, other things being equal, varies with its ripe- 

 ness, or, in other words, its state of nutrition. Abundant 

 evidence could be given to prove that there is, ns a rule, 

 an intimate relation between the nutrition of the germ- 

 cells and the nutrition of the individual in which they 

 are stored. Just as the grains of wheat may materially 

 suffer from the bad state of repair of the ship in which 

 they ai'e carried, so may germ-cells suffer when the body 

 in which they are lodged is out of condition, ill-nurtured 

 or over-strained. As the grains of wheat too early 



* As an instance of the influence of nutrition during development, I 

 may mention that I recently found that eight rabbits in one uterine horn 

 were exactly the same weight as four rabbits in the other horn. This 

 looked like a case of superfoetation, but as the eight small foetuses were as 

 well developed as tlie four large ones, the difference was evidently due to 

 the same amount of nourishment being provided for each horn regardless 

 of the contents. 



t Vernon, Roy. Soc. Proceed., May 26th, 1898. 



