XVI 



INUEODUCTIOir. 



through a distinct Nawplius stage, but when it leaves the egg has 

 the form of a Zocea, with a short carapace, often armed with 

 spines, with three eyes — a median simple eye, and two lateral 

 compound — with antennules, antennae, mandibles, two pairs of 

 maxillae, with the first two thoracic appendages well developed 

 and ending in endopodites and exopodites, but with the remainder 

 of the thoracic appendages rudimentary, and with no abdominal 

 appendages. 



Intermediate in many respects between the Crabs or Brachyura 

 and the Maeroura, are a series of forms constituting the group 

 Anomoura, a heterogeneous order comprising the hermit crabs— 

 in which the abdomen is in a soft and imperfect condition, being 

 habitually sheltered in a univalve shell, and the abdominal 

 appendages are rudimentary — and other families in which the 

 abdomen may be better developed than in the Crab, and may 

 not be permanently tucked in beneath the carapace as in the 

 latter. 



Another extensive Order of the Crustacea (the Edriophthal- 

 mata) is represented by such forms as the Sand-hoppers of the 

 sea-shore, and the "Wood-lice so common about decaying wood. 

 The body of the Sand-hopper (Orchesiia quadrimcma) is laterally 



Fia. V. — Sand-hopper (TaloreTiestia quadrimana) magnified. 

 ceph, oephalon ; per, pereion ; pi, pleon; i.-vii., segments of the pereion 

 and of the pleon ; 1-19, appendages; as, telson. 



compressed, and consists of a small head or cephalon (ceph) of a 

 thorax ox pereion (per J, consisting of seven distinct segments and 

 not covered by a carapace, and an abdomen or pleon (pi) f g j x 



