280 ZOOLOGY. 
asexual females, the males not appearing until the autumn, 
when the females lay the fertilized ‘‘ winter” eggs, which are 
surrounded by a very tough shell. Dohrn observed the de- 
velopment of the embryo in the summer eggs. At first the 
embryo has but three pairs of appendages, representing the 
antenn and one pair of jaws. It is thus comparable with. 
the Nauplius of the Copepodous Hntomostraca, and thus the 
Fig. 237.—Sida. ¢, egg in brood-sac. 
Cladocera may be said to pass through a Nauplius stage in 
the egg. 
Afterwards more limbs grow out, until finally the embryo 
ig provided with the full number of adult limbs, and hatches 
in the form of the mature animal, mndlergome no farther 
change of form. 
The members of the suborder Phyllopoda are more highly 
developed than any of the Crustacea mentioned, though, like 
the Ostracodes and Cladocera, the body is usually partly 
covered by a large carapace (the mandibular segment greatly 
developed), which is sometimes bent down, and opens and 
shuts by an adductor muscle, so that they resemble bivalve 
