86 THE BIOLOGICAL PROBLEM OF TO-DAY 



ditions must be fulfilled, as without them the 

 product never would come from the rudiment. 



That the same adults may come from the eggs 

 depends upon the egg-cells, in the ordinary course 

 of events, being in similar conditions of anabolism 

 and katabolism, being affected by gravity, light, 

 temperature, and so forth, in the same way. Thus, 

 when we are attempting to grasp the fundamental 

 nature of the course of organic development, we 

 must not omit the part played by these factors. 



We may dwell for a moment upon this weighty 

 point, as its significance is commonly misunder- 

 stood. 



The course of each organic development depends, 

 in the first place, upon the absorption and meta- 

 morphosis of matter. Inorganic matter perpetually 

 is being turned into organic material to serve for 

 the growth and development of the rudiments. 

 Thus, what in one stage of the development is mere 

 inorganic material, and an external condition of the 

 development of the rudiment, in the next stage is 

 become a part of the rudiment. The food-yolk of 

 an egg, for instance, like the oxygen of the atmo- 

 sphere, appears, in its relation to the material of the 

 rudiments, to be something supplied from outside, 

 an external condition of the development ; yet it is 

 continually passing into the rudiments and altering 

 them, even though the alteration may be purely 

 quantitative. From this follows the very simple 

 inference that during the course of an organic 

 development external matter is always being 

 changed into internal matter, or that the rudiments 



