II.] THE CRAYFISH AND LOBSTER. IQ5 



and Crayfish, two lateral spines; in the latter animal 

 it is segmented, at the point of origin of these, into 

 two portions an anterior one, the tergal surface of 

 which remains largely chitinous, and a terminal post- 

 anal one, which is completely calcified. 



The perianal area is calcified on opposite sides, to 

 form a couple of anal plates; they are most marked 

 in the Lobster. 



Note the delicate seta, which fringe the free border 

 of the telson. 



4. The appendages. 



Remove the entire set from one side of the body in 

 the order enumerated below, cutting through the 

 inter-articular membranes close to their points of 

 attachment to the axial skeleton. 



Examine under water, posterior face upper- 

 most. 



a. The third abdominal appendage. Its general charac- 

 ters have been described (i. A); examine in 

 detail 



a. Its protopodite; made up of two segments a 

 shorter proximal hip-segment or coxopodite, and 

 a long distal one (basipodite) which forms a base 

 of articulation for the exopodite and endo- 

 podite. 



y8. Its endopodite (the longer of the two terminal 

 portions). It is subdivided into two segments 

 of equal length the basal one is continuously 

 calcified, the terminal one is multi-articulate. 



y. Its exopodite; relatively shorter than (3. It also 

 is subdivided into a single basal and a terminal 



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