REPRODUCTION 281 



all the forces, constant and otherwise, which were then 

 operating. Assuming the irritability of living protoplasm, 

 any force which influences it will set up a reaction of some 

 sort in it, though this reaction may not be visible at the 

 time. Between the time of leaving the parent and meeting 

 and fusing with its mate, each sexual element was influenced 

 by and reacted to all the forces then operating. By the 

 fusion of these two living masses into one, the resultant 

 effects of all preceding influences upon the two separate 

 masses are united. From the moment of fusion, the single 

 mass is influenced by all the forces and matters, continuous, 

 constant, and variable, which constitute its environment. 

 If the fertilized egg remain within the body of the parent, it 

 is subjected, during the period of gestation, to mechanical 

 and other influences, some of which absolutely limit it in 

 form and size. For instance, the young zygospore of Spiro- 

 gyra, the young oospore of (Edogonium, the foetal colt, in 

 the body of the mother, are limited as to form and size by 

 the enclosing walls of cell or uterus. They could not grow 

 beyond a certain size, though they may never reach this 

 size, because growth would be mechanically hindered and 

 stopped by the surrounding cell or uterine walls. In form 

 also they are similarly limited, not as the mould fixes 

 the size and shape of the cast, but because, by excess- 

 ive growth in one direction or part, they would encounter 

 the mechanical resistance of the enclosing walls of cell, or 

 uterus. 



The young and forming individual, whether one-celled 

 spore or many-celled embryo, is affected also by food, 

 warmth, position with relation to gravity, etc. Of these 

 influences, we know least about the most constant. The 

 most constant influences have so far baffled the experi- 

 menter to eliminate. Since they are the most difficult to 

 eliminate, it is reasonable to conclude that they are also the 

 most powerful. If they oppose the experimenter, they must 

 also affect the young and forming individual. 



If the fertilized egg is not enclosed within the body of the 

 mother, it too is subjected to all the influences composing 

 its environment, to influences which have changed with in- 



