BRANCH ARTHROPODS: CRUSTACEANS 147 



eggs arc ready to be laid, which is during the last of 

 March or in April in the Central States, a sticky secretion 

 passes out of the openings at the base of the walking legs 

 and smears the pleopods of the abdomen. The eggs as 

 they pass out are fertilized and caught on the pleopods, 

 where they remain attached in clusters. After some 

 weeks the young crayfishes issue from the eggs. In 

 general appearance they are not very unlike the adults. 

 They grow very rapidly at this stage. As the animal is 

 enclosed in a hard shell, growth can only take place 

 during the period just following the molt, for the crayfish 

 casts its skin periodically, and it is while the new shell is 

 forming that the animal does its growing. The crayfish 

 when it molts casts not only the exoskeleton, but also the 

 lining of part of the alimentary canal. After the females 

 have hatched their young many die in the shallow pools, 

 in which places the dried-up skeletons are noticeable 



during the summer months. 







OTHER CRUSTACEANS. 



Most of the crustaceans live in water, a few being found 

 - in damp soil or in other moist places. Some are fresh- 

 water animals and some marine. They vary in size from 

 the tiny water-fleas, a millimeter long, to crabs two feet 

 across the shell or sixteen feet from tip to tip of legs. 

 They present great differences in form and general ap- 

 pearance of body, being adapted for various conditions 

 of life. Some crustaceans live as parasites on other 

 animals, in some cases on other crustaceans. Such 

 parasitic species have the body much modified and are 

 hardly to be recognized as members of the class. 



Body form and structure. In structural character and 

 body organization the Crustaceans show, of course, the 

 general characteristics already attributed to the Arthro- 



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