REINVIGORATION PRODUCED BY CROSS FERTIL- 
IZATION IN HYDATINA SENTA! 
DAVID DAY WHITNEY 
From the Biological Laboratory, Wesleyan University 
The full significance of fertilization is far from being clear not- 
withstanding a vast amount of speculation and observation upon 
both plants and animals. Darwin observed self-fertilized and 
cross fertilized plants for several generations and determined that 
cross fertilization is generally beneficial and self fertilization is 
injurious. ‘‘This is shown by difference in height, weight, con- 
stitutional vigor, and fertility of offspring from crosses and self- 
fertilized flowers, and in the number of seeds produced by the 
parent plants.” He also collected considerable data from breed- 
ers showing that the majority of them were of the opinion that 
cross breeding between individuals of the same race which lived 
in separated localities, caused an increase of constitutional vigor 
in the resulting race. 
Later Biitschl regarded conjugation in the Protozoa as a 
process involving rejuvenation and considered fertilization in the 
Metazoa in the same light. He was followed by Maupas and 
finally by Calkins who has found that the conjugation of two in- 
dividuals in a weak race of Paramoecia caused a reinvigoration 
of the race to such an extent that it was able to pass through 
another cycle of at least 376 generations before it became as 
weak as the original race from which the two conjugating indi- 
viduals were taken. 
1T am greatly indebted to the Directors of the Biological Laboratory of the 
Brooklyn Institute of Arts and Science, Cold Spring Harbor, N. Y., and of the 
Marine Biological Laboratory, Woods Hole, Mass., for their courtesies and for 
placing at my disposal private rooms and laboratory facilities during the summers 
of 1909 and 1911 respectively. 
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