CHARACTERS OF MALE AND FEMALE GAMETES 201 



animals and plants, and in nearly all the higher organisms 

 Seed Plants and a few other are exceptions the 

 male gamete or sperm is a small motile free swim- 

 ming cell, while the female gamete or egg is a large 

 passive spherical cell. The sperm is exceedingly sensi- 

 tive, at least in a large number of cases, to chemical 

 substances diffusing out from the female cell. Sperms 

 are produced in immense numbers and only a minute 

 proportion succeed in conjugating with eggs. The body 

 of the sperm cell is reduced to the smallest size compatible 

 with its function, which is to carry the paternal nucleus 

 to the egg. Its chromatin contribution to the zygote 

 nucleus is exactly equal to that of the egg nucleus 

 (see Fig. 35, F, G). The hereditary characters are 

 carried by the conjugating nuclei, and the paternal 

 and maternal chromatin are equal in bulk and equiva- 

 lent in effect on the characters of the offspring. 



The egg, on the other hand, provides in the first 

 instance the store of organic food substance with 

 which the new individual produced from the zygote 

 starts its life, and the size and passivity of the female 

 gamete are correlated with this function. The fact 

 that far fewer eggs than sperms are produced is also 

 a result of this difference in size. The first beginnings 

 of the differentiation we saw in Chlamydomonas and 

 in Pandorina. The comparatively slight difference 

 between the gametes in these forms appears as the 

 result of what may be regarded as an accidental differ- 

 ence in the rapidity and duration of the process of 

 division of the mother cell. The divisions of the 

 mother cell of the smaller (male) gametes are more 

 rapid and continue longer, so that smaller cells are 

 produced, while the divisions of the mother cell of 

 the female gametes is slower, so that larger cells are 



