34 THE ANIMALS AND MAN 



lateral pairs and a ventral pair of ostia.) Note passing 

 anteriorly from the heart along the median line to the eyes 

 a blood-vessel, the ophthalmic artery. Arising from the 

 anterior portion of the heart are the antennary arteries, run- 

 ning to the antennae. Yet another pair running anteriorly 

 from the heart to the stomach and digestive glands are called 

 the hepatic arteries. From the posterior end of the heart 

 arises the dorsal abdominal artery, running back to the telson. 

 Below this arises the sternal artery, which will be seen later. 

 In the region below the heart are located the reproductive 

 organs. They are whitish glandular masses from each of 

 which runs a tube which opens at the base of the last pair 

 of walking-legs in the male, and at the base of the third pair 

 of walking-legs in the female. 



TECHNICAL NOTE. Cut longitudinally through the dorsal wall of 

 the abdomen on either side of the median line and remove the piece 

 of shell. 



Note the powerful muscles within which flex and extend 

 the abdomen. By a rapid contraction of these muscles the 

 tail is brought beneath the body, propelling the animal 

 strongly backwards. When the crayfish crawls it generally 

 goes forward, but in swimming it reverses this direction. 



Make a drawing showing, in their natural position, the 

 internal organs which have been studied. 



Examine the alimentary canal for its whole length. Note 

 that the large bladder-shaped stomach is attached to the 

 mouth-opening by a short tube. What part of the canal is 

 this? From the posterior end of the stomach is a short 

 thick-walled part, the small intestine, followed by a long 

 straight tube, the large intestine, which opens to the exterior 

 through the anus. 



TECHNICAL NOTE. Remove the alimentary canal, detaching it 

 from the anal end first, and working forward. 



