The following points highlight the top three characters which are not heritable among animals. The characters are: 1. Acquired Modifications due to Disease 2. Characters Peculiar to Sex 3. Certain Parental Characteristics.
Character # 1. Acquired Modifications due to Disease:
Acquired modifications due to disease mutilation, use or disuse of parts, and changes due to the direct action of the environment upon the organism, such as the loss of color on the part of forms living in the dark.
Character # 2. Characters Peculiar to Sex:
Characters peculiar to sex which are inherited, not by all, but by the appropriate sex. That is, the traits which are manifested, e.g. in the case of the fatherless drone bee it will be remembered that as he inherited all of his traits—masculine and otherwise—through his mother, she must have borne all of the male characteristics within her in latent condition.
This is also shown by the fact that emasculated males are opt to show feminine traits—as with the domestic horse, wherein a gelding and a mare may make a very well-matched pair, but not as a rule either a gelding and a stallion or the latter and a mare.
It is not so much the feminine characteristics which the gelding shows as the lack of masculine characteristics which, nevertheless, are within the sum of its inheritance.
Character # 3. Certain Parental Characteristics:
Certain parental characteristics apparently not inherited, really have been received but lie in latent condition, to reappear in some future generation, as in the case of atavism.