528 



ZOOLOGY 



SECT. 



valves are opened by the elasticity of a ligament, which passes 

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

 </</// //!'//'/ iii//ndc (m.), which passes transversely from valve to valve, 

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

 of systematic value. 



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

 compound eyes are present as well. There are only seven pairs 

 of appendages. The antennuk's (f/nt.l) and antennae (nnf,.,.') are 

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

 and a nabellum-like offshoot. The first maxilla (mx.l} also bears 

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



FKI. 415. 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. aW. abdomen ; 

 K lit. 1, anteimule ; ant. 3, antenna; tl.cil. digestive gland; c. median eye; j.l, /..', thoracic- 

 feet; int. intestine ; m. adductor muscle; nid. mandible; m.r.l, <.<..', maxilla! ; of. ovary; 

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



appendage (second maxilla, ///..>'.. j*) is jaw-like in some forms 

 (Cypris) leg-like in others ( Cy there}. The only thoracic appendages 

 are two pairs of slender legs ( f.l, /.). The abdomen (abd.) is 

 devoid of appendages, and is terminated by strong seta?. 



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

 will be advisable to consider separately the free-swimming 

 Eucopepoda, the parasitic Eucopepoda, and the Branchiura. 



The free-swimming Euc<>i" i><<l<i are well represented by the 

 common water-liea (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. 



