THEORY OF FERTILIZATION. 151 



though in a different fashion in the two cases. In the progressive differentiation, 

 these two sex-cells are usually so constructed that the loss of substance in the 

 union is reduced to a minimum, hence the small mobile male and the' large 

 quiescent female cells. The union brings about a chemico-physical process, 

 which makes the female cell capable of independent nutrition and growth, and 

 evokes potential properties into actual life. 



In marked contrast to Rolph's suggestion, and the view of all 

 those who believe that the sex-cells are profoundly different, is the 

 opinion maintained by Weismann. He denies that there is a dynam- 

 ical action in fertilization. The momentous effect is merely the 

 sudden doubling of the mass of the nucleus. ' ' The physiological 

 values of sperm and egg-cell are equal; they are as 1-1. We can 

 hardly ascribe to the body of the ovum a higher import than that of 

 being the common nutritive basis for the two conjugating nuclei." 

 The external differences which are so obvious are only important as 

 means toward the conjugation of similar nuclei. "The germ-plasma 

 in the male and female reproductive cells is identical." Previous to 

 the essential moment of fertilization, half of the germ-plasma is given 

 off from the germinal vesicle of the ovum in forming the second polar 

 body. Development will not take place unless the loss be made 

 good, and the original mass restored. This is what the sperm does 

 in fertilization. In short, to Weismann the process is quantitative 

 rather than qualitative. 



This supposition appears to us to be open to criticism. (1) That the nuclei 

 are alone important in fertilization, and that the cell substance is a mere 

 adjunct, can not be said to be proved, and we have already noted some of the 

 facts which tell the other way. (2) The structure of a cell is recognized by all to 

 be an expression of its dominant protoplasmic processes. The sex-cells are 

 usually highly dimorphic, and even Strasburger allows that there may be minor 

 ■dtfferences in their nuclei, as well as the marked divergence in their cell- 

 substance. The nucleus can not be regarded as an isolated element, but as one 

 which shares in the general life of the cell. We have already interpreted the 

 differentiated male and female cells as respectively katabolic and anabolic, and 

 see no reason for doubting, in spite of structural resemblance in the rough 

 features of nuclei (all that we know), that this difference saturates through the 

 elements. (3) If the only important matter be the quantitative restoration of the 

 original amount of germ-plasma in the female nucleus, it seems difficult to 

 understand the phenomena of conjugation, whether permanent or transitory, 

 from which we believe fertilization to have originated. (4) That the normal 

 ovum should lose half its quantity of germ-plasma, only to regain a similar 

 quantity in fertilization, certainly appears a curiously circuitous process. (5) 

 The occasional possibility of inducing division by replacing the sperms with 

 other stimuli, seems to point to a dynamical or chemical action, which Weismann 

 denies. 



We are bound, of course, to admit the importance of the established facts of 

 nuclear union, and agree with Boveri that the complexity of the morphological 

 facts show the present impossibility of supposing that they can be fully expressed 



