Chap. 29 ARTHROPODS CRUSTACEANS 585 



merets and tail pieces (uropods) coating every surface. Following this prepa- 

 ration eggs pour from the oviducts and pass backward across the seminal 

 receptacle where they are fertilized. Further backward they spread out among 

 the swimmerets, and stick fast to their fringes. Crayfishes and lobsters carry- 

 ing eggs are said to be "in berry" (Fig. 29.9). The eggs of crayfishes hatch 

 in five to eight weeks but the young ones, in Cambarus — diminutives of adults, 

 are for some time fastened to the egg shells by delicate threads that act like 

 "mother's apron strings." During their first year they molt about every 12 days 

 and after that usually only twice a year, once in spring, and again in late sum- 

 mer. 



Regeneration. Crayfishes can replace lost appendages but to a lesser extent 

 than animals more simply organized. After a leg is lost, a new one appears 

 partly formed at the next molt, and larger at each succeeding molt until it is 

 complete. 



Self -amputation — Autotomy. Crayfishes and other crustaceans, especially 

 crabs, amputate their own thoracic legs. If a leg is injured or grasped it may 

 be suddenly snapped off at a definite breaking place, on the basal segment 

 of the great claw or at the third joint at the other legs. Across the inside of the 

 leg on the proximal side of the breaking place there is a partition with a small 

 hole in the center through which nerves and blood vessels extend to the tip of 

 the leg. When the leg is cast off the hole is quickly stopped by a blood clot. 



Molting and Hormones. A crayfish sheds a hard exoskeleton that fits tightly 

 and will not stretch. It appears in a new one that is soft and elastic, and ad- 

 justable to increased size (Fig. 29.14). The old skeleton was brittle with cal- 

 cium; the new one contains relatively little of it. 



Molting is a laborious process during which every smallest spine and fila- 

 ment of the gill is pulled from its old cover. As it proceeds, the molting animal 

 uses more and more oxygen until the shedding is over. Then, for a time, it is 

 weak and helpless. There are profound adjustments in the metabolism of cal- 

 cium in preparation for the discard of the old skeleton and the completion 

 of the new one. For some time previous to the molt, a quantity of calcium 

 from the old exoskeleton is absorbed and distributed by the blood especially 

 to the stomach where it is deposited in the gastroliths (Fig. 29.14). Experi- 

 ments prove that the formation of the gastrolith is under the control of an 

 endocrine gland. After molting, the cuticle of the new exoskeleton is hardened 

 by calcium brought from the gastroliths by the blood as well as from new sup- 

 plies absorbed from the surrounding water. Most arthropods absorb unusual 

 quantities of water before molting. This swells their bodies, helps to split the 

 old exoskeleton and partly accounts for the sudden enlargement of the "soft- 

 shelled" animal. 



An endocrine secretion limits the number of molts. It is produced by the 

 minute sinus glands, one in each eyestalk of crustaceans which have eye stalks; 



