152 THE BIOLOGY OF THE ANIMAL 



possible the relative position of these various 

 parts, and make a drawing of the eye. 



c. The ear. — Among the bunches of setse on the basal 



joint of an antennule find, by using a fine bristle, 

 the opening into the auditory organ. Leave the 

 bristle inserted and, using it as a guide, cut away 

 the under side of the joint with a scalpel. Close 

 examination will reveal a small transparent sac, 

 the auditory sac, lying among the muscles with- 

 in the joint. Dissect this out. How large is it ? 

 Examine under the low power in a drop of water 

 or glycerine. What is the shape of the sac? 

 Color ? Cut it open. Do you find sand-like par- 

 ticles or otoliths inside? Notice also the setas 

 or auditory hairs. What is their position? 

 Shape ? Relation to the otoliths ? 

 Draw the sac, otoliths, and setae. 



d. The olfactory setae. — Examine with the lens the 



under surface of each joint of the endopodite of 

 the antennule for setce. Are these at all different 

 from those found at the edges of the segments? 

 Draw. 



Iiite7'nal Anatomy. — The various systems are given in 

 the order in which they are most conveniently examined. 

 Take a second specimen, and with a pair of strong shears, 

 being careful not to injure the organs lying beneath, cut 

 through the exoskeleton along each side of the body 

 from the telson to the rostrum. Begin at the anterior 

 end of the abdomen and, working back, carefully remove 

 the upper half of the shell by cutting the muscles with 

 a sharp scalpel at their points of attachment, noting par- 



