THE CRAYFISH. 27 



joints, and the motions allowed by each. With the 

 forceps seize the squarish, basal segment of this leg, 

 and pull off the leg. 



7. Remove in like manner the leg in front of this, again 

 being careful to get a firm hold of the short, wide 

 segment next to the body. What is the relation 

 between the leg and the gill nearest to it? Lay this 

 leg on a paper in front of the one previously removed. 

 In this way pull off all the legs of one side, from the 

 hindmost to the foremost, laying them in order. 

 Compare them all with the one first taken. In the 

 legs bearing pinchers is there any really new part 

 added, or is the pinching apparatus produced by some 

 change in a part present in all the legs? How do 

 the legs which bear the big claws differ from the 

 walking legs ? Compare them, segment with segment. 



8. In front of (anterior to) the big legs are several pairs 

 of appendages surrounding the mouth. Probe be- 

 tween them to find the mouth. These mouth parts 

 are numbered from the front, but on account of the 

 way in which they overlap, it is easier to remove and 

 study them in the reverse order. 



9. The appendages just in front of the big claws are the 

 hindmost of three pairs of jaw-feet, or maxillipeds. 

 Gently raise them, to see how they cover the other 

 mouth parts. Note that these maxillipeds, or foot- 

 jaws, have an inner branch, which meets the corre- 

 sponding part of the opposite maxilliped, and an 

 outer branch. Observe that both these branches are 

 attached to one segment next to the body. Seize this 

 basal segment, and remove the whole maxilliped. 

 Compare it with one of the swimmerets of the third 



