1 66 ARTHROPOD A 



It returns from the gills to the cardiac sinuses, pericardial sinus and 

 back through the ostia to the heart. There are valves in the arteries 

 and sinuses. 



Respiration is by means of gills. Astacus, the crayfish found 

 west of the Rockies, has i8 pairs; the lobsters have 20 pairs and 

 Cambarus, east of the Rockies, has only 17 pairs. 



Excretion. — Paired, flattened " green-glands " are found in the 

 ventral region of the head near the esophagus. 



Reproductive System. — Ordinarily the sexes of the lobster and the 

 crayfish are separate, although Turner has recorded many interesting 

 cases of hermaphroditism in the crayfish. The essential organs of 

 reproduction in the male are the bilobed testis, the paired vasa 

 deferentia transporting the sperms to the outside, and the modified 

 abdominal appendages, called stylets, which are used to transfer 

 the spermatozoa to the ventral pouch (seminal receptacle) of the 

 female. 



In the female, the bilobed ovary sends off eggs which pass from 

 the paired oviducts and are fertilized by spermatozoa stored in the 

 ventral pouch at the time of conjugation, sometimes months pre- 

 viously. A lobster from 8 to 10 inches long produces from 3,000 

 to 100,000 eggs in a season. The crayfish may produce 2,000 eggs in 

 a season. Each egg is attached to one of the swimmerets and 

 hatches in about two months, the larvae undergoing two or three 

 moults before they leave the mother, and moulting 8 times the first 

 summer. 



The Nervous System consists of a l^rain (two cerebral ganglia) 

 and a ventral nerve cord with esophageal connectives uniting the 

 cerebral ganglia and the nerve cord in the sub-esophageal region. 



The ventral cord shows by the great number of concentrated 

 lateral nerves as well as by the marked enlargement in the anterior 

 thoracic region that the right and left halves of the ventral cord 

 have fused. To a limited extent this fusion is evident in the ab- 

 domen. 



The ganglia of the last three cephalic and the first three thoracic 

 segments have united forming a large compound sub-esophageal 

 ganglion. Between the fifth and sixth thoracic ganglia the ventral 

 nerve cord is separated widely to permit the passage of the sternal 

 artery which runs dorsi-ventrally. There are 12 ganglia belonging 

 to the nervous system. The brain supplies the eyes, antennae and 

 antennules. (Figure 74.) 



