3<> 



CRUSTACEA. 



Fig. 9 A. cd, is the edge of the thorax ; sue I is the 

 sternal plate of the first pair of maxillae, which is normally 

 a double plate forking to form sockets for the bases of 

 the metastomata (////), whose broad extremities (//// i) lie 

 upon the mandibles (b) ; ;// is the triangular mouth, and 

 lb the labium or anterior lip, with three pairs of imperfectly- 

 formed plates : sub, the sternal plate of the mandibles. 



Kig. 9 A. 

 mi 



ad 3 - 



Teachers who consult Huxley's " Crayfish,*' Eng. Ed., 

 Fig. 39, p. 153, and descriptions, will see at once that he 

 unites the first pair of maxillae to the thorax, considering 

 the sternal plate to be represented by the first sternum of 

 the united thoracic sterna. This would bring the division 

 of the head from the thorax between the first pair of max- 

 illas and the mandibles. This is probably an error arising 

 from defective observation. The sternal plate {sue 1) can 

 be detected only by careful work on account of its imperfect 

 calcification in young crayfishes, but is readily seen in the 



