108 



FRESHWATER ANIMALS 



MIDDENDORFIANA 



Fig. 10. Structure and distribution of Daphnia middendorffiana Fischer 

 and D. pulex Leydig and of populations that appear to be hybrids between 

 them. In a broad belt between the northern region where middendorffiana is 

 one of the few species of Daphnia and the southern region where pulex is 

 common, neither of these species is found in its "pure" form. In this belt 

 there are many populations, the individuals of which have some character- 

 istics of both middendorffiana and pulex. 



