THE BEARERS OF THE HERITAGE 305 
individual differences of such organisms. In this connection it is a 
significant fact that in young hybrids between two distinct species the 
early stages of development, especially as regards symmetry and 
regional specifications, are exclusively or predominantly maternal in 
character, but the male-influence becomes more and more apparent as 
development progresses until the final degree of intermediacy is 
attained. 
From the evidence at hand this much seems sure, that the paternal 
and maternal chromosomes respectively carry substances, be they 
ferments, nutritive materials or what not, that are instrumental in 
giving the final parity of personal characters which we observe to be 
equally heritable from either line of ancestry. It is clear that most 
of the characters of an adult organism cannot be merely the outcome 
of any unitary substance of the germ. Each is the product of many 
codperating factors and for the final outcome any one codperant is 
probably just as important in its way as any other. The individual 
characters which we juggle to and fro in our breeding experiments seem 
apexed, as it were, on more fundamental features of organic chemical 
constitution, polarity, regional differentiation, and physiological 
balance, but since such individual characters parallel so closely the 
visible segregations and associations which go on among the chromo- 
somes of the germ-cells it would seem that they, at least, are repre- 
sented in the chromosomes by distinctive codperants which give the 
final touch of specificity to ‘those hereditary characters which can be 
shifted about as units of inheritance. 
Sex and heredity.—Whatever the origin of fertilization may have 
been in the world of life, or whatever its earliest significance, the 
important fact remains that to-day it is unquestionably of very great 
significance in relation to the phenomena of heredity. For in all 
higher animals, at least, offspring may possess some of the character- 
istics originally present in either of two lines of ancestry, and this 
commingling of such possessions is possible only through sexual repro- 
duction. As has already been seen, in the pairing of chromosomes 
previous to reduction, the corresponding members of a pair always 
come together so that in the final segregation each gamete is sure to 
have one of each kind although whether a given chromosome of the 
haploid set is of maternal or paternal origin seems to be merely a 
matter of chance. Thus, for instance, if we arbitrarily represent the 
chromosomes of a given individual by ABC, abc, and regard A, B and 
C as of paternal and a, , and ¢ as of maternal origin, then in synapsis 
