CRUSTACEANS $7 



Observe the position of the eyes (Figs. 8i, 88). How long 

 are the eyestalks ? Is the stalk flexible or stiff ? Touch the 

 eye. Where is the joint which enables the stalk to move ? 

 Is the outer covering of the eye hard or soft ? A mounted 

 preparation of the transparent covering (cornea) of the 

 eye, seen with lower power of microscope, reveals that the 

 cornea is made up of many divisions, called facets. Each 

 facet is the front of a very small eye, hundreds of which 

 make up the whole eye, which is therefore called a com- 

 pound eye. The elongated openings to the ear sacs are 

 located each on the upper side of the base of a small feeler 

 just below the eye. 



Respiratory System. — The respiratory organs are gills 

 located on each side of the thorax in a space between the 

 carapace and the body (Fig. 87). The gills are white, curv- 

 ed, and feathery. Is the front gill the largest or the smallest? 

 The gills overlap each other; which is the outermost gill ? 

 On the second maxilla is a thin, doubly curved plate called 

 a gill bailer (Fig. 85). The second maxilla is so placed 

 that the gill bailer comes at the front end of the gill 

 chamber. The bailer paddles continually, bringing the 

 water forward out of the gill. The gills are attached 

 below at the base of the legs. Are the gills thick or thin ? 

 How far upward do they go ? Does the backward motion 

 in swimming aid or hinder the passage of the water through 

 the gills ? Does a crayfish, when at rest on the bottom 

 of a stream, have its head up or down stream ? Why ? 



Openings. — The slitlike vent is on the under side of 

 the telson (Figs. 82, 88). The mouth is on the under side 

 of the thorax behind the mandibles. At the base of the 

 long antennae are the openings from the green glands, two 

 glands in the head which serve as kidneys (Fig. 89). 

 The openings of the reproductive organs are on the third 



