324 General Biology 



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

 in biology speak of an otocyst ( ), but the newer ones 



have discarded this name entirely ; for that organ, which 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 statocysts 

 are 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, however, 

 be either a sense of touch, or taste, or smell. 



MUSCULAR SYSTEM 



As the crayfish possesses an exoskeleton, all of the muscles are 

 attached to the interior of its casing. The strongest muscles are in the 

 abdomen. It is by means of these that the abdomen can be bent quickly 

 and easily, producing a powerful stroke in the water and shooting the 

 body backward rapidly. All of the appendages are also supplied with 

 muscles. The muscles are very beautifully arranged, though quite com- 

 plicated and rather difficult to work out. 



REPRODUCTION 



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

 The male (Cambarus) possesses tri-lobed testis (one pair lies anteriorly 

 and a single lobe lies posteriorly) in which the spermatozoa arise. The 

 spermatozoa pass through the vasa deferentia ( ) 



out of the paired genital openings in the last pair of thoracic legs. 



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 

 time. The female exudes a sticky substance upon the swimmerettes 

 after lying upon her side for several days and cleaning and polishing 



