CRUSTACEA. 27 



normally on the sides, and when brought by function 

 into opposition, and used to cut and grind against 

 each other, they must necessarily move from the sides 

 towards the middle. Taken collectively, the mandi- 

 bles, maxilla;, and maxillipeds are called the mouth- 

 organs on account of their proximity to that opening, 

 and because some of them do assist in preparing the 

 food which has been found upon the ground, and which 

 has been caught and killed by the big arms. When 

 the closely applied edges of the mandibles are sepa- 

 rated, the interior of the mouth is exposed, and just 

 above it is the soft labrum or upper lip ( big. 9 A, //>). 



in front of and above the mandibles are the long 

 feelers or antennae (Figs. 6, 7, %j^n 2). and ne^t to 

 these the short antennas ( yigpSWjfir&rO- <* 0- I-astly, 

 the eyes (Fig. 6, cy) are s/erPat the ends of stoiffc ' 

 movable stalks on either site* of the projecting ros-'^ \ 

 trum of the carapace. V J 



The pupils have now founH^f^irft'cn pans of'ap-/ 

 pendages in the cephalothorax, imoS^U£>^uesti(»n will 

 be sure to arise in some of their minds, Are these ap- 

 pendages borne upon rings like those of the abdomen, 

 and if so, where are the rings? It is evident they are 

 not on the outside, therefore search must be made for 

 them on the inside. Most young people will be in- 

 tensely interested in answering this question, and will 

 eagerly remove one side of the carapace, and cut off 

 tie feathery gills which obstruct their view, to see 

 whether the walking-legs are fastened to anything they 

 may call rings. They will discover what appears to be, 

 at first sight, a white, thin wall extending along the 

 sides of the cephalothorax, but which, upon closer 



