IBT10 i LUVIATILIS 205 



being alone visible. These, and the two pairs which lie im 



me -li.-ii.-lv under or in front of them, are called maxillipede*, 

 or " fol-jaw>." The next tw<> pairs, delicate and lo!i;n 

 tre the maxilllB j \\liile beneath or ratlin- in front of thriii 

 an- two strong, toothed orpins, tlir mandibles. These, the 

 maxilla* and the maxillipedes, thus constitute six pairs of 

 gnathites. 



The remaiiiiiii; three pairs of ;i ppendages occupy the 

 of the forepart of the eephaio-thoiax, in front of thr inouili. 

 The most posterior pair, or the long feelers, are the antenn;i-; 

 tin- next, or the short feeln>, are thr antennuhe; while the 

 most anterior pair ate the movable stalks, which -uppnrt tin- 

 eyes upon their extremities the "ophthalmic peduncles," or 

 "ophthalmites." 



To arrive at an understanding of the composition of thi> 

 complex body with its multiform appendages, we must first 

 detach and study carefully one of the abdominal segment > 

 say the third. Such a segment is nearly semi-circular in ver- 

 tical section, the dorsal wall, or tergum, being very con 

 and where it reaches the level of the almost straight ventral 

 wall, or sternum, sending down a flattened loin-, which is re- 

 flected at its free edges into a corresponding prolongation of 

 the ventral wall, so that each infero-lateral angle of the seg- 

 ment is prolonged into a hollow process, thr plniroii. Near 

 the outer extremities of the straight ventral portion of tin- 

 segment two rounded articular cavities, which receive the 

 basal joints of the appendages, are situated. A transverse 

 groove will be seen on the tergum, separating rather more 

 than the anterior third of its surface, as a smooth, coi. 

 lenticular facet, which is completely overlapped by thr ]>-- 

 terior margin of the preceding segment, Waen the alidomm 

 i> extended, and is left uncovered only in complete flexion. 

 This is the tergal facet. A corresponding flattened and rath- 

 er excavated Surface upon the anterior half of the pleuron, 

 which is similarly overlapped by the preceding pleuron, and 

 is left uncovered onlv in complete extension, mav lr termed 

 the pleural facet. It will be ol>-< rvrd that there is a close 

 correspondence between the skeleton of an abdominal somite 

 of a (Y.iv-lish, and that of a thoracic somite of a Trilol> 

 except that, in the latter, tin' sternal re 



The appendages of the segment (Fi_-. ', 1 . A' W 

 pie, consistinir of a cylindrical basal portion, divided into two 

 joints, a shorter proximal, and a longer di-i:il. to the latt- 

 which two terminal manv-jointed filaments are articul;: 



12 



