CRUSTACEA 55 



transferred to her. In some species the females have a 

 small pouch in the exoskeleton (the annulus) into which 

 the spermatophore is thrust by the male. 



A female has an ovary in the thorax which connects by 

 two short ducts with openings in the basal segments of the 

 third pair of walking legs. After receiving a spermato- 

 phore she prepares with great care to lay eggs. The 

 abdomen and its appendages are cleaned for two or three 

 days by scraping them with the last pair of walking legs. 

 The female then lies on her side, bends the abdomen a little, 

 and secretes a gelatinous apron over the underside of the 

 body (Fig. 29). The eggs are then ejected from the opening 

 in the third legs; the spermatophore dissolves and the 

 sperm cells "fertilize" the eggs inside the gelatinous apron. 



The jelly of the apron soon shrivels and breaks up; the 

 eggs becoming fixed to the abdominal appendages by little 

 stalks. The mother crayfish takes good care of the eggs; 

 they are kept clean and frequently aerated by elevating 

 the abdomen and waving the appendages which bear them 

 (Fig. 29). There is yolk material stored within each egg- 

 shell to nourish the developing embryo until it hatches. 

 When the little crayfish emerges, it is attached to the old 

 egg-shell by a slender filament which issues from the anus. 

 It remains thus fastened to the mother even after its first 

 moult (Fig. 30), but when the skin is shed the second time, 

 the little creature is free and soon able to shift for itself. 

 A female crayfish carries from three to six hundred eggs 

 at a time and after becoming mature usually breeds 

 annually. A crayfish usually lives to be six or seven years 

 old. 



A mature crayfish reacts to its surroundings so as to be 

 successful as long as possible, and thus continue its race. 

 How much mental ability does it display in responding 

 to the stimuli which it receives ? Very little. Its behavior 

 is largely made up of reflexes and instinctive activities. 

 If a large object appears in its field of vision, the crayfish 

 crouches down into its crevice; if a small animal moves, 



