56 



BEGINNERS' ZOOLOGY 



to its mouth (Figs. 85, 86). They are in form and in use 

 more like fingers than feet. In front of the foot jaws are two 



pairs of thin jaws 

 (maxillae) and in 

 front of the thin 

 jaws are a pair of 

 stout jaws (mandi- 

 bles) (Fig. 85). Do 

 the jaws move 

 sidewise or up 

 and down ? Which 

 of the jaws has a 

 jointed finger (palp) attached to it? Do all the appen- 

 dages for taking food have both exopod and endopod 

 branches on a basal stalk or protopod ? Which of the 

 appendages have a scalloped edge? How would you know 

 from looking at the crayfish that it is not merely a 

 scavenger ? Why are there no pincers on the hind feet ? 



Sense Organs. — Find the antewicu, or long feelers (Figs. 

 82, 90). Are the antennae attached above or below the 

 eyes ? (Fig. 87.) 



Fig. 87. 



•Gill cover removed and gills exposed. 

 Mp, gill bailer. 



r r 



Fig. 88. — Lengthwise Section of Male Crawfish. 



c, heart; Ac, artery to head; A a, artery to abdomen; Km, stomach; D, intestine; 

 L, liver; T, spermary; Co, opening of sperm duct; G, brain; iV, nerve chain. 



Find the pair of antennulcs, or small feelers. Are their 

 divisions like or unlike each other? Compare the length 

 of the antennules and the antennae. Compare the flex- 

 ibility of the antennae with that of the other appendages. 



