132 CRAYFISH, LOBSTEKS, SPIDERS, AND INSECTS 



which were desciibed as pacliUehke organs attached to the 

 second maxihte, play back am I forth ha the anterior openings 

 of the gill chambers and propel the water forward out of 

 the chambers. This causes the fresh water, Ijearing oxj'gen, 

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

 tinuous currents over tiie gills. 



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

 just noted, is given up )j\' 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 urinary 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. — Tb.e sexes are separate 

 and the abdomen of the female is nruch broader than that 

 of the male. The ovary is situated aliove 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 b}' the female to her smmmerets. 

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

 to the swimmerets in berrylike clusters. After some weeks 

 the yovmg era}' fish issue from the eggs but remain attached 

 to the s^l'immerets for some time. Thej^ attain a length 

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

 later years gi'ow more slowly and rarely l^ecome 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' wlien the body is being pulled out of its old skin. 

 In either case, new ones wn\\ readily grow out again. When 

 a leg is l)roken off, tlie blood quickly coagvilates at the broken 



