The Cellular Basis 197 



egg and of the developed animal are found in the cytoplasm. No 

 doubt the differentiations of the 'cytoplasm of the egg as well as 

 the peculiar form and structure of the spermatozoon have arisen 

 during the genesis of these cells under the influence of paternal 

 and maternal chromosomes contained within their nuclei, just 

 as in the differentiation of any tissue cell; but in the case of the 

 spermatozoon these cytoplasmic differentiations are lost when it 

 enters the egg, whereas those of the egg persist. In short on- 

 togeny begins in the egg before fertilization whereas the sperm 

 can influence ontogeny only after, and usually a considerable 

 time after, it enters the egg. 



The fact remains that at the time of fertilisation the hereditary 

 potencies of the two germ cells are not equal, the polarity, sym- 

 metry, type of cleavage, and the pattern, or relative positions mid 

 proportions of future organs, being foreshadowed in the cyto- 

 plasm of the egg cell, while only the differentiations of later de- 

 velopment are influenced by the sperm. In short the egg cyto- 

 plasm determines the early development and the sperm and egg 

 nuclei control only later differentiations. 



We are vertebrates because our mothers were vertebrates and 

 produced eggs of the vertebrate pattern ; but the color of our skin 

 and hair and eyes, our sex, stature, and mental peculiarities were 

 determined by the sperm as well as by the egg from which we 

 came. There is evidence that the chromosomes of the egg and 

 sperm are the seat of the differential factors or determiners for 

 Mendelian characters, but the general polarity, symmetry and 

 pattern of the embryo are egg characters which were determined 

 before fertilization. But these egg characters, like any other 

 character of the female, were probably determined by chromo- 

 somes derived from her father and mother; if so they are Men- 

 delian characters inherited by the mother through her chromo- 

 somes and carried over to the first filial generation, not as factors 

 but as developed characters. Such cases may be called "maternal 

 inheritance" since the characters come only from the egg, or "pre- 

 inheritance" since these egg characters are developed before fer- 

 tilization. (See pp. in, 112.) 



