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Page:Popular Science Monthly Volume 61.djvu/45

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THE PHYSICAL BASIS OF HEREDITY.

part of others it is looked upon as a means of rejuvenescence or union of energies to insure the continuance of life for another span. Loeb has found that an egg that will under all normal conditions develop only after a male cell has entered it, may be caused to develop without the male cell by placing it for a short time in a solution of higher osmotic pressure than that in which it is normally found. It is thus seen that one function of the male cell is either to supply stimulation to the egg to cause it to develop, to regain the lost power of dividing, to rejuvenate it or to act as a catalyzer. But it has long been known that the child may inherit from the father. Indeed, Boveri has shown that the male cell can also develop alone into a new individual if it is supplied with a proper medium of sufficient size.

PSM V61 D045 Egg reproduction.png

Fig. 9. a. Larva of Sphærechinus granularis. 6. Larva of Echinus microtuberculatus. c. Hybrid of Sphærechinus egg and Echinus sperm, showing blended characters, d. Fragment of Sphærechinus egg, fertilized with an Echinus sperm, showing paternal characters only.

The egg and the sperm are thus seen to equally contain the hereditary tendencies necessary to form a new individual. Since the offspring frequently resembles both parents this result is evidently caused by the mingling of the two hereditary tendencies.

Boveri's experiment brings us naturally to the question as to where in the hereditary cells the power of reproducing all the complicated transmissible parts lies. In spite of the fact that it is inconceivable that the many hereditary qualities of, say an elephant, should be compressed into two cells, one just large enough to be seen with the unaided eye and the other far too small to be seen without the microscope, he has demonstrated that the hereditary plasma is restricted even to certain parts only of these cells.