124 CRUSTACEANS, 



swimmerets. The young, when hatched, are nearly a 

 quarter of an inch long, almost transparent, and in struc- 

 ture show much resemblance to the adults. The points 

 of their forceps are variously hooked, enabling them the 

 better to hang on to the maternal swimmerets. In the 

 process of development, molting takes place several times. 

 The carapace splits down the back, and the animal crawls 

 out limp and defenseless. It has great difficulty in with- 

 drawing its legs, and sometimes breaks them off ; but new 

 ones will grow out from the broken stumps. Specimens 

 will be found occasionally with one forceps smaller than 

 the other : the smaller one is replacing one that has been 

 lost. 



The time of each molt is a critical period in the life of 

 the animal ; for when its hard coat of mail is gone, its 

 muscles overwrought with the struggle of extrication, and 

 even its defensive weapons soft and pliant, it becomes an 

 easy prey to even its weaker enemies. It therefore seeks 

 the closest seclusion at such times. 



The exuvia of the crawfish is not broken in molting, 

 except by the one longitudinal slit ; and after the animal 

 emerges, the edges of this slit come together again elas- 

 tically, and the exterior looks much as it did before the 

 molting. The hard parts of the stomach are shed also 

 at every molt. 



Crawfishes live a number of years. They grow rapidly 

 during the first season, after attaining a length of an inch 

 and a half. They grow more slowly in later years, and 

 rarely attain a length of more than five or six inches. 



Crawfishes belong to the group Crustacea. 



Other Crustaceans. Two other very common crusta- 

 ceans are excellent subjects for study here, as they illus- 

 trate important differences in crustacean structure. 

 These are the Asellus and the Cyclops. 



