FIG. 72. DIAGRAM OF THE EXTERNAL FEATURES OF THE FRESHWATER 



CRAYFISH, Antaeus fliwialilis. 



The student is recommended to take as a simple practical lesson a careful 

 study of this or some similar type. See Huxley's Crayfish an Introduction 

 to Zoology. 



At the anterior end in front of the stalked eyes is the rostrum (/?). The 

 antennules ( Al) bear tactile and olfactory setae and have a balancing ear 

 at their base. The long antennae are organs of touch. Then, on the 

 under surface, there are six pairs of appendages (mandibles, two pairs of 

 maxillae, and three pairs of nlaxillipedes) crowded around the mouth. 



The cervical groove (CG) is the boundary-line between the head portion 

 of the crayfish and the thorax portion. The shield that covers both these 

 parts is called the cephalothoracic shield. Its posterior side-Haps (GC) 

 Eorm the gill-covers protecting the eighteen pairs of gills. 



The forceps (F) and the walking legs (WL) are obvious. The posterior 

 part of the body, called the. abdomen (ABD), consists of six segments and 

 a terminal plate or telson (T), on the ventral surface of which the food- 

 canal ends. On the underside of the abdomen there are appendages called 

 swimmerets, and the last or nineteenth pair oi appendages form the paddles 

 (P) on each side of the telson. 



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