THE PHYSICAL BASIS OF HEREDITY. 



39 



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 with- 

 out 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. 



Fig. 9. a. Larva of Sph,erechinus granclakis. 6. Larvaof Echinus microluberculatus. 

 c. Hybrid of Sphcerechinus egg and Echinus sperm, showing blended characters, d. Frag- 

 ment of Sphcer echinus egg, fertilized with an Echinus sperm, showing paternal characters only. 



The egg and the sperm are thus seen to equally contain the hered- 

 itary tendencies necessary to form a new individual. Since the off- 

 spring 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 com- 

 pressed into two cells, one just large enough to be seen with the un- 

 aided 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 colls. 



