THE CRAYFISH 



151 



right-hand member of this pair should be compared part by part with 

 the walking leg just examined. It has the same parts, except that an 

 exopodite is present. In one region two of the segments have fused 

 to form a single one as in the cheliped. This third maxilliped is a very- 

 important appendage for purposes of comparison, because it still has 

 the fundamental plan, and so can be compared with the simpler abdom- 

 inal appendages; the structure of its endopodite shows how one may 

 interpret the adult structure of the walking leg. Draw this appendage 

 oriented as above. 



(f) Examine, without removing, the second maxillipeds which lie 

 in front of the third. They will be found to have parts similar to the 



Fig. 67. — Young American lobster, Homarus americanus, at a stage when 

 exopodites are present on the pereiopods. 



(From F. H. Herrick, 1895, Bulletin V. S. Bwrcau Fisheries.) 



latter. Remove the right second maxilliped with care not to destroy 

 the first maxilliped which lies close in front of it. Identify, without 

 removing, the parts of the first maxilliped. There is a large epipodite 

 which lies in the gill chamber just behind the bailer. Protruding to- 

 ward the mid-line are two thin flaps which are outgrowths from the 

 protopodite, and at about right angles to these are two other projec- 

 tions which are the exopodite and endopodite. Which is which? 

 Kemove the right first maxilliped and draw on a large scale, orienting 

 as above. 



(g) The remainder of the appendages occur on the head. Anterior 

 to the first maxillipeds are two pairs of maxillae, the parts of which 

 should all be identified before removal is attempted. Each of the 

 second maxillae has a four-parted protopodite, a delicate endopodite, 



