2O4 GEORGE W. TANNREUTHER. 



female-producing female, fertilization is ineffective and the female 

 continues to reproduce parthenogenetically. In the male-pro- 

 ducing female, after impregnation takes place, either all resting 

 eggs are formed or male and resting eggs. The alternating of 

 the two kinds of eggs cocurs more frequently when few sperm are 

 present in the oviduct. 



The uterus of the male-producing female may contain embryos 

 ranging from early cleavage to late development (Fig. 2), but 

 if at this point impregnation occurs, yolk spherules are formed 

 within the vitellarium and all of the following eggs formed 

 become true resting eggs. Maturation of the male and resting 

 eggs occurs immediately after their separation from the ovary 

 at the end of the growth period. 



The sperm of the sexually mature males before their birth 

 (Fig. 7, m.e.2) may be deposited into the uterus of the parent 

 and bring about the production of resting eggs (Fig. 7, r.eg.} 

 as above. In case of the extreme degenerate males (B, 11-15 

 and Fig. 7, m.e.i) the sperm sac and the delicate body wall break 

 down, the sperm are set free in the uterus and the production 

 and fertilization of the resting eggs follow. Again the sperm 

 sac (B, 15) with the delicate body wall (degenerate male) may 

 be deposited intact into the water and later the mature sperm 

 are set free and finally get into the uterus of the different indi- 

 viduals. The independent entrance of the sperm is rather a 

 simple process, since the urinogenital sinus and the lower end 

 of the uterus is constantly being partially everted and inverted 

 and during these activities the sperm make their entrance into 

 the uterus. One of the peculiar activities of the normal male 

 is the occasional eversion of the lower end of the vas deferens and 

 discharge of the mature sperm into the water. The entrance of 

 the sperm into the uterus independently of the male is a common 

 method in this particular rotifer and makes possible the fertiliza- 

 tion of a greater number of resting eggs. Those instances in 

 which the male embryos and the resting eggs alternate in the 

 ' same uterus, are often due to the later method, where sperm 

 enter at different intervals. 



The free-swimming males are rather scarce, less than one 

 per cent, at any time, when compared with the total number of 



