440 Transactions of the Society. 



re-arrangemeuts of the characters displayed by the ancestry, as we 

 see in a piebald pony or in a hybrid cockatoo. Now, it does not 

 seem very difficult to imagine the origin of this kind of quantita- 

 tive variation. Without pinning our faith as yet to any very 

 detailed view of the material basis of inheritance, we may regard it 

 as certain that the chromosomes play an exceedingly important 

 part as vehicles of the heritable qualities. We may compare 

 them to a microscopic pack of cards, and we know that they are 

 sometimes visibly ditferent from one another in the same germ- 

 cells, and that there is an extraordinarily elaborate shuffling of 

 the cards before development begins. In the reduction-process 

 involved in the maturation of the egg-cell, half of the ovum's pack 

 is thrown away, usually in the first polar body, and comes to 

 nothing. In the maturation of the spermatozoa there is also a 

 halving of the pack, but all the reduced units are in this case 

 functional. In fertilization the two half-packs come together in 

 intimate and orderly union, though without fusion of chromosomes, 

 forming the zygote-nucleus. The opportunities for permutations 

 and combinations of hereditary items, and for the dropping out of 

 one or more altogether, are obvious. Thus the origin of variations 

 of a quantitative sort does not seem beyond our power of con- 

 ception, except in the sense that we do not in any way under- 

 stand cell-division, whether meiotic or equational. 



§ 5. A separate consideration may be given to fertilization as 

 a source of variation, a view prominent at one stage in the develop- 

 ment of Weismann's theories. For a time he was inclined to 

 attach great importance to the mingling (or amphimixis) of two 

 sets of hereditary qualities as a possible source of novelties, but 

 he afterwards attached more importance to the influence that 

 somatic fluctuations in nutrition might have in inducing changes 

 in the germ-j)lasm or in inducing struggle among the analogous 

 hereditary items. In recent years the botanist Lotsy has been 

 a thorough-going champion of the variational significance of ferti- 

 lization, and has gone the length of maintaining that all variation 

 is due to crossing. That this is a very extreme view is shown by 

 the occurrence of variations in parthenogenetic lineages, but there 

 is ample experimental evidence that novelties may be induced 

 by crossing. This is not surprising when we remember that two 

 very complex systems of dual origin become in fertilization a 

 unity that goes on in most cases to develop into a harmonious life. 



§ 6. The problem before which we are baffled is the origin of 

 the distinctively new, where the novelty is qualitative not quanti- 

 tative. Some would refuse to admit this distinction, and perhaps 

 they are pedantically right : the distinction is one of common 

 sense. There is many a grade between those who find their 

 fingers indispensable in simple computations and the calculating 

 boy who can tell us in a few seconds the cube root of 17,073,512, 



