536 



ZOOLOGY 



SECT. 



The eyes (a) are large, compound, arid raised on movably articu- 

 lated stalks. The antennules (c^) and antennae ( 2 ) are large, the 



mandibles (md.) have palps 

 (mt), and the exopodite of 

 the second maxilla (mxt) 

 has the form of a slender 

 filament which acts as a 

 " cleaning-foot " to keep the 

 cavity of the carapace free 

 from foreign bodies. There 

 are eight thoracic append- 

 ages (brf ), all of them leaf- 

 like, and recalling those of 

 Apus. The first four abdo- 

 minal appendages {pi p4) 

 are large biramous swim- 

 ming-feet, like those of 

 Copepods; the fifth and 

 sixth (p5, p6) are small 

 and uniramous. 



The Schisopoda (Fig. 423) 

 are small transparent, 

 shrimp-like forms, mostly 

 from 2-6 mm. in length. 

 They agree with the Crayfish 

 in the general form of the 

 body, in the union of the 

 head and thorax, in the 

 presence (except in Ana- 

 spidcs) of a carapace which 

 may, however, leave some of 

 the posterior thoracic seg- 

 ments uncovered and in the 

 number both of segments 

 and appendages, but present 

 several interesting charac- 

 ters indicating a lower grade 

 of organisation. One of the 

 most notable of these is the 

 absence of differentiation in 

 the thoracic appendages, 

 which have a leg-like and 

 not a leaf-like form, but 

 which are all alike, none of 



them being modified into maxillipedes, except to a very slight 

 degree in some forms. Moreover the legs all possess exopodites 



, eye 



FIG. 422. Nebalia geoffroyi, mal 



uj, antennule ; 2 > antenna ; c, head; />//, thoracic 

 feet; <l, intestine; h. heart; kin, gizzard ; ,n<i. 

 mandible ; mt, mandibular palp ; mnt. exo- 

 podite of second maxilla ; pi p, pleopods ; 

 r. rostrum ; s, carapace ; x,n, adductor muscle ; 

 t. testis ; / VIII, thoracic segments. (From 

 Lang's Comparative Anatomy, after Claus.) 





