LIFE-HISTORY OF ROTIFER 



TABLE 2—Conchided 



235 



d indicates daj' of death. 



In most of the species of rotifers, the males differ markedly 

 from the females; they are smaller, shorter-lived, much more 

 active than the younger females, and are usually degenerate in 

 structure, lacking complete excretory or digestive systems. But 

 in Proales werneckii the male is of the same size as the female 

 and resembles her externally. On this account it seemed in- 

 advisable to rely on appearances alone as to whether the form 

 under observation in Proales decipiens was male or female, but 

 if on isolation eggs were deposited it was clear that the individual 

 was female. The appearance of two types of eggs, thin-shelled 

 and thick-shelled, early in the history of the race suggested 

 that at that time males might be present and the thick-shelled 

 eggs deposited by a fertilized female. This suggestion wa§ 

 supported further by the fact that the thick-shelled eggs did not 

 appear during the second v/inter, as they perhaps would had 

 they been merely 'winter eggs.' Early in the experiment it was 

 noticed that in the usual culture fluid of j^ per cent malted 

 milk, all individuals isolated for any exiDcriment produced eggs; 

 that is, in malted milk no males appeared. In the case of 



