132 CRAYFISH, LOBSTERS, SPIDERS, AND INSECTS 



which were described as paddleUke organs attached to the 

 second maxillae, play back and forth in the anterior openings 

 of the gUI chambers and propel the water forward out of 

 the chambers. This causes the fresh water, bearing oxygen, 

 to flow into the chambers from below, thus producing con- 

 tinuous currents over the gills. 



Method of excretion. — The carbon dioxide, as we have 

 just noted, is given up by the blood in the gills. In ad- 

 dition, there are two green-colored excretory organs, the 

 so-called green glands, situated in the head, just in front 

 of the stomach. Each organ consists of a cushion-shaped 

 gland and a thin-walled sac, or lu-inary bladder, that opens to 

 the exterior by a duct which has its mouth on the ventral 

 side of the basal segment of the antenna. 



Reproduction and life history. — The sexes are separate 

 and the abdomen of the female is much broader than that 

 of the male. The ovary is situated above the anterior 

 end of the intestine and below the- heart. The eggs 

 are laid the last of March or in April, at least in the central 

 states, and are glued by the female to her swimmerets. 

 The eggs are small, spherical, and dark colored and adhere 

 to the swimmerets in berryUke clusters. After some weeks 

 the young crayfish issue from the eggs but remain attached 

 to the swinmierets for some time. They attain a length 

 of about an inch and a half the first season, but during the 

 later years grow more slowly and rarely become over five 

 or six inches long. 



Regeneration of lost parts. — The large legs of the cray- 

 fish are often lost in fighting and sometimes the legs are 

 broken off when the body is being pulled out of its old skin. 

 In either case, new ones wiU readUy grow out again. When 

 a leg is broken off, the blood quickly coagulates at the broken 



