212 



MANUAL OF ZOOLOGY. 



Fig. 68. Lsemodipoda. Caprella phasma. 



taceans, which are distinguished amongst the Edriophthalmata 

 by the rudimentary condition of the abdomen. The first 



thoracic segment is amal- 

 gamated with the head, 

 and the limbs of this seg- 

 ment appear to be inserted 

 beneath the head, or, as it 

 were, beneath the throat 

 (fig. 68) ; hence the name 

 given to the order. The respiratory organs are in the form of 

 two or three pairs of membranous vesicles attached to the 

 segments of the thorax, or to the bases of the legs. The 

 L&modipoda do not swim, and one section of the order com- 

 prises parasitic Crustaceans, of which the Whale-louse ( Cyamus 

 Ceti) is the most familiar. 



ORDER II. AMPHIPODA. The members of this order resemble 

 those of the preceding in the nature of the respiratory organs, 

 which consist of membranous vesicles attached to the bases of 

 the thoracic limbs. The first thoracic segment, however, is dis- 

 tinct from the head, and the abdomen is well developed, and is 

 composed of seven segments. There are seven pairs of thoracic 

 limbs, directed partly forwards, and partly backwards, the name 

 of the order being derived from this circumstance. 



Fig. 69. Amphipoda. The Sand-hopper, Talitrus Zocusta, enlarged. 



All the Amphipoda are small, the " Sand-hopper" (Talitms 

 locusta, fig. 69) and the "fresh-water Shrimp" (Gammarus 

 pulex] being two of the commonest forms. 



ORDER III. ISOPODA. In this order the head is always dis- 

 tinct from the segment bearing the first pair of feet. The 

 respiratory organs are not thoracic, as in the two preceding 

 orders, but are attached to the inferior surface of the abdomen, 



