218 



Arthropoda, Glass 1. Crustacea, 



Most of the members of this group are active organisms swimming 

 and hopping about in the water ; the former is effected by means of 

 the first three pair of abdominal limbSj the 

 latter by the flexure of the caudal appendage. 

 Other forms {see below) are less energetic. 

 Numerous species and individuals are marine, 

 occurring on the shore as well as in deeper 

 water, and in the open sea. A few are fresh- 

 water ; some live among seaweed of the shore, 

 or far from the coast on damp ground. A 

 few are parasitic. 



Fig. 180. Transverse section of the thorax of Gam- 

 mams (enlarged). 1, 2 first and second joints of a leg, and 

 brood pouch ; b one of its constituent laminae, g gill, 

 h heart, o ovary, t gut, I liver, n ventral ganglion. — Adapted 

 from Sars. 



1. The Presh-water Shrimp (Gammarus) may be taken as a repre- 

 sentative of the typical Amphipod. Eyes fairly small, second and thii-d thoracic 



Fig. 181. 1 — 2 Caprella acuUfrons, from above and from the left. 3 Cyamus 

 TOj/sticeti, from above. Ill — FIJI Thoracic segments. 4 j first antennae. Ca Rudimentary 

 abdomen, g gill, K^' — Kg second — eighth thoracic legs. — 1, 2 after Mayer, 3 after Liitken 

 (adapted). 



