Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 HEREDITY AND PROTOPLASM 459 chromosomes into two groups is called the reduction division, since it reduces the mimber of chromosomes. In the formation of sperm cells also a reduction division occurs. But instead of producing polar bodies the sperm mother cell forms four sperm cells. The polar bodies formed by the maturing of the ^g^ cell die and disappear. When a sperm cell unites with an egg cell in fertilization, the resulting zygote contains the full number of
Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 HEREDITY AND PROTOPLASM 459 chromosomes into two groups is called the reduction division, since it reduces the mimber of chromosomes. In the formation of sperm cells also a reduction division occurs. But instead of producing polar bodies the sperm mother cell forms four sperm cells. The polar bodies formed by the maturing of the ^g^ cell die and disappear. When a sperm cell unites with an egg cell in fertilization, the resulting zygote contains the full number of chromosomes, Fig. 245. The formation of an egg cell The chromatin material of the nucleus network, /, arranges itself into a definite number of chromosomes, 2, which divide up into two equal groups, 3. Half of the chromosomes are pushed out of the cell, 4, and form the first polar body,/. The chromosomes of the polar body, as well as the chromosomes remaining in the mother cell, split lengthwise, and half of each chromosome is pushed out, 3. The first polar body thus becomes two bodies, /^ and /.21 and the mother cell puts out a third polar body, /g, retaining half the original number of chromosomes. This cell is now the egg cell half derived from the male parent and half from the female parent. From all the evidence that is now available it would seem that the chromosomes are the features of the germ cell which bear whatever it is that determines the development of the characters that distinguish the individual from others of the same species, and at the same time those characters that identify it with others of the same species. 481. The germ plasm and acquired characters. According to August Weismann (1834-1914) each organism is what it is because it developed from a certain germ plasm. When this organism produces new germ cells, it merely transmits
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