380 



CRUSTACEA ENTOMOSTRACA. 



spring and summer, the females produce the so-called summer 

 eggs, which contain a large quantity of oil globules and are 



surrounded by a delicate 

 vitelline membrane. 

 They develop rapidly 

 within the brood-pouch 

 between the shell and the 

 dorsal surface of the 

 mother, and after the 

 space of only a few days 

 develop into a fresh 

 generation of young 

 Cladocera, which escape 

 from the brood-pouch. 

 The embryonic develop- 

 ment takes place accord- 

 ingly under extremely 

 favourable conditions, 

 which depend upon the 

 rich supply of food yolk 

 in the large eggs, and 

 sometimes upon addi- 

 tional food material 

 secreted within the 

 brood-pouch. 



At the season when 

 the males appear, the 

 females, independently of 

 copulation, begin to pro- 

 duce so-called winter 

 eggs, which are incap- 

 able of developing with- 

 out fertilization. The 

 number of these winter eggs is always relatively small. They 

 are distinguished from the summer eggs by their larger size and 

 the greater quantity of food yolk, and their formation in the ovary 

 is accompanied by much more extensive processes of absorption. 

 Before the eggs pass into the brood-pouch, the walls of the 

 latter, which as above stated are formed by the dorsal and pos- 

 terior portions of the bivalve shell, become modified over a 



FIG. 252. Appendages of Daphnia (after Claus). 

 , anterior antenna of male ; b, maxilla ; c, first leg 

 of female, c', of male; rf,a leg of the 2nd pair ; Br 

 bract ; Ex exopodite. 



