OTHER THEORIES OF SPECIES-FORMING. 307 



searches, to be the chief agent in constructive processes of the cell, 

 it equally appears to be incapable of life, or unable to act in a 

 normal manner, when removed from the influence of other cell 

 substances. The food required by a germ-cell for its growth is 

 obtained from without the cell, and must pass through the cytoplasm, 

 in more or less changed condition, to reach the chromatin within 

 the nucleus and there be elaborated into living substance and 

 passed over to the cytoplasm in other form. This conclusion is 

 drawn from both experimental and microchemical studies. So the 

 oxygen required by the cell, and the water, must be obtained from 

 without the cell. This is simply in agreement with the general 

 principle that no body can increase in mass, circumambient condi- 

 tions remaining unchanged, without accretions from outside. 

 Therefore, the germ-plasm does not so much create new substances 

 as it changes substances brought to it. It and the other cell con- 

 stituents are harmoniously and mutually interdependent, and the 

 ultimate source of energies of these substances, all connected with 

 the elaboration of living matter, is referable to external agencies 

 because referable to food. 



''This being the case, the energies of the hereditable substance, 

 the germ-plasm, are clearly dependent upon influences of the envi- 

 ronment. This conclusion is not at all in contradiction with the 

 idea of the continuity of the chromosomes, as we pointed out in 

 the preceding chapter. Therefore, Weismann was in error when, to 

 support his idea of the continuity of the germ-plasm, he at first 

 argued the energies of the germ-plasm to be independent of body 

 cells and of the environment generally. His supposition was both 

 unnecessary for the view of the continuity, and also out of agree- 

 ment with the phenomena. The ovum cannot elaborate its yolk 

 substance except out of food substance received from without ; 

 the amount of its food substance will depend upon the state of 

 nutritive metabolism of the individual carrying the egg-cell ; starva- 

 tion of that individual will cause cessation of energy in the germ- 

 cell, and ligaturing of the blood-vessels supplying the ovary will 

 produce death of the egg-cells. The results of observational expe- 

 rience teach that the germ-plasm is not a little god, capable of self- 

 existence without respect to external agencies, but is very intimately 

 bonded to the latter. Whether the germ-cell, as in the sponges, be 

 an amoeboid cell which wanders about in the body tissues, or 

 whether it is immovably held in place by tissue-cells, it is impossi- 

 ble that it can live and grow without receiving and reacting to 

 stimuli from these tissue-cells. The egg-cells of many animals are 

 set free in water before they commence to cleave into embryonic 

 cells; how can we say, then, that the conditions in the water do 



