XI 



PHYLUM ARTHROPODA 



527 



female and the posterior part of the carapace is a large 'brood- 

 pouch (t>r.'p\ in which the eggs are stored. The paired eyes 

 (E) have fused into a single organ, which exhibits a constant 

 trembling movement. The antennules (ant.l) are small, the 

 antenna? (ant.2) very large, biramous, and constitute the chief 

 organs of locomotion. The mandibles arc large, the second 

 maxillae absent in the adult, and there are five pairs of leaf-like 

 swimming-feet (/) on the thorax. The abdomen is devoid of 

 appendages. Many of the Cladocera have an extraordinarily 



FIG. 414. Three Cladocera. an.t.l, anteiinule ; n,it.>, antenna ; In: brain ; in-.-fi. brood-pouch; 

 E. eye; il.f/l. digestive gland; /. swimming-feet; Id, heart; nn.l. mandible; sh.rtl. shell- 

 gland. (1 after Clans, 2 and 3 after Gerstaeeker.) 



grotesque form (2, 3), owing to the peculiar shape of the head, the 

 immense antenna?, and the great hump-like brood-pouch. 



The Ostracoda are usually not more than 1-2 mm. in length, 

 and are found both in fresh and sea-water. One of the commonest 

 genera is Gypris, which occurs in immense numbers in stagnant 

 pools. Cythere is a common marine form. 



The body (Fig. 415) is unsegmented, and is completely enclosed 

 in a carapace (A), the right and left halves of which are articu- 

 lated together along the dorsal edge so as to form a bivalved shell 

 (C), which may be variously ornamented or sculptured. The 



