146 THE BIOLOGY OF THE ANIMAL 



shape and size of each of these segments, and ex- 

 amine particularly the manner in which they are 

 connected and the direction of motion at each 

 joint. Can you find an opening, the male geni- 

 tal aperture, in one of the segments? Into 

 which of the segments does it open ? 

 Draw this appendage. 



Eemove the next appendage, being careful not to 

 remove the gill attached to the articular membrane, 

 and compare with this. Do you find that it has all of 

 the segments named above? Does it extend in the 

 same direction as the other ? Notice that it also bears 

 two parts not found on the other, a gill and a plate- 

 like expansion, the epipodite. Where and how are 

 these parts attached ? Notice in female specimen of the 

 lobster the opening of the receptive apparatus near 

 the base of the coxopodite. Draw. . Eemove the second 

 from the last appendage and compare with the other two. 

 "Which does it more closely resemble ? Does it bear a 

 gill and an epipodite ? Note how the dactylopodite is 

 attached to the propodite, forming with the latter a pair 

 of pincers or a chela. Look for an opening, the female 

 genital pore, in the coxopodite of this appendage. 

 Draw. Compare the next appendage with the preced- 

 ing, noting aU the resemblances and differences. Draw. 

 Eemove the great chela or pincers and compare 

 with the other appendages, noting especially the great 

 size of the segments. Are the two chelse shaped alike? 

 If not, do you find on examining a number of specimens 

 that the great chela of the right side has certain con- 

 stant characters and that of the left also ? Are the 

 two chete of the same size? Do you find any ex- 

 treme difference in the size of the two chelse on the 

 same animal? If so, how do you explain? Do you 



