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long straight intestine is the hind-gut or proctodaeum. The 

 greater part of the gut is lined with cuticle, the only part 

 lined with endoderm being the mesenteron. 



The front or " cardiac " chamber of the stomach is a 

 gastric mill with ossicles and teeth ; and there the food 

 is ground fine and passed through a sieve of setae into the 

 *'' pyloric " chamber. Two large and branched digestive 

 glands open by two ducts into the mesenteron where the 

 food is digested. 



Above the intestine is the pericardium, a large space in 

 which the dorsal heart is suspended. The heart has three 

 pairs of openings (ostia) through which it receives blood 

 (purified in the gills) from the pericardium. 



Behind the bases of the antennules are the cerebral or 

 pre-oesophageal ganglia, connected by a wide nerve-ring 

 with the first ganglia of the ventral nerve cord. In the 

 thorax the cord is double and lies in the tunnel of the 

 endophragmal skeleton. There are six pairs of thoracic 

 ganglia and six abdominal ganglia. 



There is a " green gland " or kidney behind the base of 

 each antenna. The gonads are situated beneath the peri- 

 cardium, and are three-lobed (Y-shaped) organs in both 

 sexes. The vasa deferentia (of the male) are long coiled 

 ducts which issue, one at each side, from the junction of 

 the three lobes, and which open on the coxopodites of the 

 last walking legs. The oviducts (of the female) are short, 

 and the external openings are on the second pair of legs. 



The greater part of the abdomen is occupied by thick 

 ventral flexor and thinner dorsal extensor muscles. 



What is the general Course of the Blood Circulation in the 



Crayfish ? 



The impure blood is collected in irregular spaces (haemo- 

 coele) and passes to the gills. The purified blood returns 

 from the gills, ma, the pericardium, to the heart which drives 

 it to the body through muscular- walled arteries. From 

 the heart a median dorsal ophthalmic artery and two 

 antennary arteries pass forward ; and, outside these, two 

 ehort hepatic arteries. Posteriorly the heart gives off a 

 vessel which at once divides into a dorsal abdominal artery 



