The earliest living units, according to Prof.
lung, were presumably smaller and simpler It is assumed that and other physico-chemical conditions came into existence. Woo bred, be sk, that some representatives of these earliest beginnings.
Tu these early and more primitive units, Professor McClung indicated, the germ plasm was in close contact with the environment. Bi organisms grew in size and complexity the germ plasm came to be surrounded by other parts or organs so that, except for penetrating X-rays and other forms of radiation, they are: well protected from immediate contact with the external world, and are thus less likely to be influenced by the outside environment.
In the ancestral primitive form of life, Dr. 'McClung believes, the' germ plasm exercised a more direct control of the body substance around it. As size and complexity increased, other forms of control evolved, such as the nervous system and the hormones that are so important in body functioning. As the body cells became more highly specialized in their outer parts, the nuclear part might become more limited in its potentialities. Therefore, he decláred, in higher animals and plants the nuclear controls are possibly limited to a few of the more basic functions.
In the germ cells of the sex glands, however, Dr. McClung explained, the germ plasm retains its full capacity, so that new individuals may be produced without any loss of potentialities due to the elaboration of the body.
Genes are known to affect not only a single character, but also the whole organism, and they may produce effects at different stages in embryonic development. To be successful, any body changes brought about by gene changes must be harmonious with the existing organization and the environmental conditions. Therefore, evolution has been a slow process.
Prof. McClung concluded that it would require much more study of the interrelationships between germ-cell structure and body structure and between genes and the changes in development before one can gain a thorough understanding of all the underlying principles involving the functioning of the germ plasm within the body of an animal or plant and also an understanding of the way in which this germ plasm has evolved from simple beginnings.
Text read from the printed page and cleaned; old type leaves the occasional error.