THE ARTHROPODA 



It is doubtful whether the crayfish can hear. Some of the older texts 

 speak of an otocyst ( ), but the newer ones have 



discarded this name entirely, for that organ, \vhich was supposed to be 

 used for hearing, has come to be considered a balancing organ by which 

 the animal knows whether or not it is right side up and which, thereby, 

 makes it possible for the crayfish to adjust its position and direction. 



These little chitinous lined sacs on the basal segment of each anten- 

 nule are now called statocysts ( ).. There are a 



number of sensory hairs in this sac and a few grains of sand called stato- 

 liths. These latter are placed there by the crayfish itself. These little 

 sand grains coming in contact with the sensory hairs make it possible 

 for the animal to determine its direction and position while swimming. 

 The statocysts are therefore called organs of equilibrium. The statocyst 

 is shed whenever the animal molts. 



We do not know whether the crayfish has a definite sense of smell 

 or not. When meat juices or tiny particles of meat are so placed in 

 the water that a slight current carrying some of the meat comes close 

 to the animal's feelers, it begins working its jaws. This may be either 

 a. sense of touch, or taste or smell. 



MUSCULAR SYSTEM 



As the crayfish possesses an exoskeleton all of the muscles are at- 

 tached to the interior of its casing, the strongest ones being in the abdo- 

 men by which that part of the body can be bent quickly and easily, 

 producing a powerful stroke in the water and shooting the body back- 

 ward rapidly. All of the appendages likewise are supplied with muscles. 

 The muscles are very beautifully arranged, quite complicated and rather 

 difficult to work out by the student. 



REPRODUCTION 



Crayfish are dioecious, that is, the two sexes are separate (Fig. 209). 

 The male (cambarus) possesses tri-lobed testis (an anterior pair and a 

 single posterior lobe) in which the spermatozoa arise which pass through 

 the vasa deferentia ( ) out of the paired genital 



openings, in the base of the first abdominal appendage. 



In the female there is a bi-lobed ovary in which the eggs are found. 

 These, upon ripening, pass through the parent oviducts out of the genital 

 openings, one of which is located in each base of the third walking leg. 

 The sperm are transferred from the male to the seminal receptacle of 

 the female during copulation, which takes place most frequently in the 

 autumn. The seminal receptacle itself is a cavity in the fold of the 

 cuticle between the fourth and the fifth pairs of walking legs. 



The eggs are usually laid in April and probably fertilized at that 



