XI PHYLUM ARTHROPODA 57:! 



from one to another at tlip, hinge, and are closed by a large 

 adductor muscle (m.), which extends transvurselj^ from valve to valve, 

 its insertions giving rise to markings on the shell (A, ?».), often 

 of systematic value. 



At the anterior end is a median eye («), and in some forms 

 compound ej^es are present as well. There are only seven pairs 

 of appendages. The antennules (ant.l) and antenna=! (ant£) are 

 large and uniramous. The mandible (md.) has a large leg-like palp 

 and a flabellum-like offshoot. The firsi maxilla (mx.l) also bears 

 a large plate resembling a flabellum of Apus. The last cephalic 



Fig. 450. — A, external view of CypriS ; B, the same with the appendages exposed by the removal 

 of the left valve of the shell ; C, transverse section ; D, a single sperm, abd. abdomen ; 

 ant.l, antennule ; ant^, antenna; iLffl. digestive gland; e. median eye; j'.l, //:, thoracic 

 feet; j'vi/. intestine ; m. adductor muscle; ti/d. mandible; mx.l, my: S, maxilLr ; or. rivary ; 

 ah. shell ; t. testis. (After Gerstaecker.) 



appendage (second maxilla, 7nj:::.') is jaw-like in some forms 

 (Oypris),\eg-]ike in others (Gythere). The only thoracic appendages 

 are two pairs of slender legs (f.l, f:3). The abdomen (tibd.) is 

 devoid of appendages, and is terminated by a pair of small 

 caudal styles. 



The diversity of form among the Gopepoda is so great that it 

 will be advisable to consider separately the free-fiwi mining 

 Eucopepodn, the parasitic Eucapcpodfi , and the Branchiurn. 



The free-swimming Eucopcpoda are well represented by the 

 common water-flea {Cyclops), found everywhere in fresh and 

 brackish water, and easily recognisable, in spite of its minute 

 size, by its elongated form, its rapid, jerky movements, and by the 

 egg-sacs of the female. 



