158 ELEMENTS OF COMPARATIVE ZOOLOGY. 



abdominal somites with those of the third. In the male 

 they are peculiarly modified. What numerical relations do 

 you find between somites and appendages in the abdomen ? 

 (Savigny's law). 



Examine the lower surface of the cephalothorax, and 

 see if you can find traces of segments, especially in the 

 region near the abdomen. How many appendages on one 

 of these somites ? How many pairs of large legs, includ- 

 ing the " pincers," do you find ? In the hinder pair of legs 

 how many joints do you find ? Can you distinguish exop- 

 odite and endopodite ? Compare this leg, joint by joint, 

 with the big claw. What change would make it into a 

 pinching-organ ? How many of these legs are furnished 

 with pincers ? Look on the inside of the basal joints of 

 the legs for openings (outlets of the reproductive organs). 

 If they occur on the middle pair the specimen is a female; 

 if on the last pair it is a male. What is the sex of your 

 specimen ? 



Study the appendages (mouth-parts) in front of the big 

 claws. In order to do this properly it will be necessary to 

 remove those of one side one by one, by grasping the base 

 of the appendage with the forceps and pulling it out. 

 Be careful to get all of each appendage, and nothing 

 else. The three hindermost (or outer) mouth-parts are the 

 jaw-feet (maxillipeds). Compare the hinder pair with the 

 third swimmeret. Do you find basiopodite, exopodite, and 

 endopodite? Compare it with one of the walking-legs. 

 Which part, exopodite or endopodite, is lacking in the 

 latter ? Draw each of the maxillipeds. 



In front of the maxillipeds come two pairs of accessory 

 jaws (maxillae). Eemove them carefully, and draw. 

 Look on the hinder maxilla for a large expansion, the gill- 

 bailer. Kemoving these parts exposes the mouth, on 



