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THE AMERICAN NATURALIST [Vol. XLIV 



maximum of extreme proportions and falling away again with 

 equal or greater abruptness with accompanying high death rate 

 and appearance of sexual reproduction, especially in rotifers, 

 seem to be of a similar nature to the cycles with intervening 

 depression periods in laboratory cultures. These occur, more- 

 over, constantly and with surprising regularity in nature, in 

 both marine and fresh-water plankton anions organisms of short 

 life-cycles. 



Certain points in both Schaudinn's and Hertwig's theories of 

 sexual reproduction are combined with the earlier suggestions 

 of Biitschli in a theory of sex which has much in common with 



in consistency concerned with the dynamic activities such as cell 

 division and locomotion, the other more solid, the reserve stuff 

 for the activities of life. In cell division these substances are 

 not equally distributed, reserve stuff predominates in some 

 (females) and the locomotor substance in others (males). 

 Morphological cell constituents for these substances are expressly 

 not postulated. An indifferent protozoan by division gives rise 

 to equal numbers of differentiated male and female individuals, 

 whose differentiation increases as division progresses. Fertiliza- 

 tion takes place in consequence of the physico-chemical attraction 

 of the two substances. The same chemical differences which 



Dr. Doflein's book is not only a great mine of carefully and 

 critically assembled information on Protozoa, but bis facts are 

 marshaled with reference to the great problems underlying all 



CELEBRATING DARWIN'S GREATNESS AND 

 DARWINISM'S WEAKNESS 



It will seem less ungracious now that the year has turned, 

 the one-hundredth year since Darwin's birth and the fiftieth 



