162 



THE MOKPHOLOGY OF THE COMMON CRAYFISH. 



getlier with the sudden widening of the same parts in 

 the j)osterior cephalic somites, gives rise to the lateral 

 depression (fig. 39, cf) in which the scaphognathite lies. 

 The limit thus indicated corresponds with that marked 

 by the cervical groove upon the surface of the carapace, 

 and separates the head from the thorax. The three pair 

 of maxillipedes (7, 8, 9), the forceps (10), the ambulatory 



Fig. 43. — Astacus fluviatilis. — Long-itudinal section of the anterior part 

 of the cephalothorax ( x <j). I — IX, sterna of first nine cephalo- 

 thoracic somites; i, eyestalk ;2, basal joint of antennule ; 5, basal 

 joint of antenna ; 4> mandible ; a, inner division of the masticatory 

 surface of the mandible ; a', apophysis of the mandible for muscular 

 attachment ; cj), free edge of carapace ; e, endostemite ; eyij)!, endo- 

 pleurite ; cpi7i, epimeral plate ; 1, labrixm ; m, muscular fibres con- 

 necting- epimera with interior of carapace; mi, metastoma ',2*^1'' 

 procephalic process. 



