no ECONOMIC ZOOLOGY AND ENTOMOLOGY 



male each segment of the abdomen, except the last, bears a 

 pair of appendages or swimmerets. The first two pairs are 

 modified to serve as channels for the sperm fluid. The last 

 pair of appendages is broad and flat and with the last segment, 

 the telson, forms the broad tail, or swimming fin. In the 

 female the first two pairs of abdominal appendages are very 

 small or altogether lacking. 



The food, which for the most part consists of vegetable 

 matter, or dead organic matter, passes into the stomach 

 through a short esophagus. The stomach is divided into two 

 parts. The anterior portion, the cardiac chamber, contains 

 three strong teeth, the gastric mill. These grind the food 

 before it passes back through a fine strainer of stiff hairs into 

 the second or pyloric chamber, which receives the secretions 

 from the large digestive glands that surround the stomach. 

 The intestine is a straight tube opening to the outside by a 

 slit-like anal opening on the under side of the telson. 



The heart lies in the pericardial sinus in the posterior 

 portion of the cephalothorax. The contractions of the heart 

 force the blood out into seven arteries which carry it to all 

 parts of the body. The ophthalmic artery supplies the eyes 

 and other parts of the head. The two antennary arteries 

 supply the antennae, excretory organs and other tissues. The 

 two hepatic arteries supply the digestive glands. The dorsal 

 abdominal artery supplies the intestine and surrounding 

 tissues. The sternal artery passes down to the ventral wall 

 where it divides, one part carrying blood to the appendages in 

 the thorax and the other part to the appendages of the abdo- 

 men. All of the arteries give off many branches which divide 

 again and again into very small capillaries which open into 

 spaces between the tissues. From all of the tissues the blood 

 finally makes its way to a large space, the sternal sinus, in the 

 ventral part of the thorax. From the sinus it passes out into 

 channels in the gills where it gives off its carbon dioxide and 

 receives oxygen from the water which bathes the gills. Then 

 through other channels, the branchio-cardiac sinuses, it 

 reaches the pericardial sinus which surrounds the heart. 

 From here it enters the heart through three pairs of openings, 



