HARD PARTS OF THE COMMON CRAB. 



179 



c. Notice now on each side of the rectangular mouth 

 area, or peristome, a large orilice which communicates with 

 a capacious chamber under the carapace. 



This chamber is the branchial chamber, and the aperture 

 is that through which the water passes from the gills. 

 Lying in the mouth of this aperture, notice a thin, mem- 

 braneous, spoon-shaped scoop, the scaphognathile, by the 

 movement of which, 

 during life, the water 

 is bailed out of the 

 branchial chamber. 



Fia. 94. — Outer sur- 

 face 6f left first maxilli- _ 

 ped ; natural size. (Drawn CK 

 from nature by W. K. 

 Brooks. ) 



Letters as in Fi?. 92. 



Fig. 91. 



erh 



d. Raise up the edge of this scoop, and notice that it is 

 part of a thin, membraneous 

 appendage, the second maxiUa 

 C2E-|^\i \ ex\ ^^ (Fig. 95). 



Fig. 9.5. — Outer surface of second 

 maxilla; natural size. (Drawn from 

 nature by W. K. Brooks, ) 



sc. Scaphognathite. Other letters as 

 in Fig. 92. 



Remove this appendage for examination, and notice that 

 Jthe two divisions of the protopodite (h) and {ex) are 

 [elongated, bilobed, and hairy. The lobes of the basipo- 

 idite (b) are long and slender, while those of the coxopo- 

 Jdite are more rounded. Outside these notice a short, 

 pomted, hairy process (en), which is the rudimentary 



Fig. 95. 



