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 

 (i<!<fuctor muscle (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 (e), and in some forms 

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

 of appendages. The antennules (ant.l) and antennae (ant. 2) are 

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

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

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



FIG. 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. <ibd. abdomen ; 

 ant.l, antennule ; ant.3, antenna; d.gl. digestive gland; e. median eye; f.l,f.2, thoracic 

 feet; int. intestine ; m. adductor muscle; mil. mandible; mx.l, mx.2, maxillae; ov. ovary; 

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



appendage (second maxilla, mx.2) is jaw-like in some forms 

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

 are two pairs of slender legs ( f.l, f.2). The abdomen (dbd.) 

 devoid of appendages, and is terminated by strong setae. 



ns 



r 



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

 will be advisable to consider separately the free-swimminj 

 Eucopepoda, the parasitic Eucopepoda, and the Branchiura. 



The free-swimming Eucopepoda are well represented by th< 

 common water-tiea (Cyclops), found everywhere in fresh am 

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

 size, by its elongated form, its rapid, jerky movements, and by th< 

 egg-sacs of the female. 



