74 POPULAR SCIENCE MONTHLY. 



mensely varied and complex. Autophagy explains the sexual act as a 

 process by which sexual cells mutually devour one another. Each is 

 fed to the other and by mutually contributing their substance both make 

 possible the energy exhibited by the fusion cell. 



Autophagy conceives the sexual cell (gamete) as one that lacks 

 the energy of its progenitor, the asexual element. It is a cell reduced 

 and starved. Ordinarily its vitality is at such a low ebb that further 

 development is impossible. Sometimes it is not so far gone but that a 

 favorable environment will induce parthenogenetic growth. The sex- 

 ual cell may be brought back to virile activity with power to propagate 

 the race, if supplied with the necessary energy. And the simplest 

 method of attaining this end, according to autophagy, is the coopera- 

 tive union of these weakened elements, a mutual feast, which revives 

 the worn-out protoplasm and enables the fusion products to make a 

 fresh start. 



The hypothesis of autophagy may be attacked from several points, 

 and becomes very unsatisfactory when so examined. It is crude and 

 entirely insufficient to cover the subtle phenomena that it attempts to 

 handle. The cause of the fusion of gametes involves problems of 

 chemistry and physics which can only be investigated by methods of ex- 

 treme delicacy and precision. One may see at a glance that conjuga- 

 tion is not the same as the actual feeding of one unicellular organism 

 upon another. In such a case, which might be illustrated with many 

 Protozoa, the captive form is destroyed and its dead substance is then 

 worked over through elaborate changes into the protoplasm of the 

 living cell. In the conjugation of sexual cells, the two masses of pro- 

 toplasm fuse and mingle and perhaps the most significant feature of 

 the process is the union of the two sexual nuclei. 



As a matter of fact, sexual cells are, generally speaking, well 

 nourished, and in all higher organisms the egg is specially provided 

 with food, far above the amount ordinarily present in cells. The un- 

 fertilized egg does not lack food, but is unable to command the neces- 

 sary energy or, if such be present, it is tied up in some form that can- 

 not be used. The importance of the latter condition is indicated by 

 the investigations of Dr. Loeb, who found that a slight increase in the 

 density of sea-water will induce the immediate development of the un- 

 fertilized eggs of sea urchins, star fishes and a certain worm. In the 

 earlier experiments, salts of magnesium and potassium were added to 

 the sea- water, but later studies have shown that sugar induces similar 

 parthenogenetic development. It is suggested that merely the with- 

 drawal of water from the egg by osmosis is sufficient to cause its de- 

 velopment without sexual intervention. And it may be supposed that 

 normally the sperm brings to the egg substances that excite such con- 

 ditions within the egg that water is given off. But we are far from 



