Introdiictio7i to A nimal Morphology. 361 



the freshwater shrimp, has a large antennule and a mandi- 

 bular palp. Lysianassa has no prehensile feet. Chelura 

 terebrans bores into submerged timbers, 2. Hyperidfe — 

 marine, often of extraordinary shapes ; head large, thick ; 

 antennae often rudimental ; second maxilla three-jointed ; all 

 the limbs are prehensile, and the uropoda form a swimming 

 tail ; the body is not bent as in Gammaridse, so they cannot 

 leap. Phronima has only one pair of antenna). 



Order 4. Isopoda {Lalreille) — integument membranous, 

 rarely calcified ; segments nearly homonomous, dorsally com- 

 pressed ; the two hinder thoracic limbs and the five abdominal 

 legs equal, ambulatory ; the post-abdominal feet lamellose ; 

 maxillipede forming a lower lip ; the intra-ovular Nauplius has 

 two trefoil-like side processes, representing the carapace, 

 spines and gills of Zoea, but on emission from the egg the larva 

 only differs from the adult by wanting the fifth abdominal 

 pair of legs ; the embryo in the egg is ventrally turned, as in 

 Schizopods, not dorsally, as in Amphipods or most Decapods ; 

 the first thoracic segment is free from the head, except in 

 Praniza, where the three thoracic segments and head unite ; 

 the gills are attached to the pleiopoda, each of which has ex- 

 ternal to it an epipodial membrane, which is delicate and 

 respiratory in the aquatic, thick, tile-like protective in the 

 terrestrial forms ; the antennae are four ; the eyes often close 

 together ; the eggs are sometimes carried in brood-pouches 

 attached to the legs ; there is a mandibular, but no maxillary 

 palp. 



The following families are included : — i. Pranizidae — with 

 two large pair of antennce ; head and thorax fused ; last 

 pleiopod and telson forming a tail ; ambulatory limbs five 

 pairs ; thoracic rudimental ; the young and the female Praniza 

 are suctorial and parasitic ; the adult male is free, and has 

 been described under the name Anceus. 2. Bopyridae — male 

 small, jointed ; female broad, eyeless, unsymmetrical, with no 

 mandibular palp, and a rudimental mouth ; parasitic on other 

 crustaceans (shrimps) ; males attached to the females, as in 

 Siphonostomata. Bopyrus has in the female lamellose pleio- 

 pods ; lone has branched threads ; Liriope is parasitic on 

 the parasite Peltogaster; Cryptonisus is planaria-like, with 



