294 CIVIC BIOLOGY 



kill the occupants. The Biological Survey has designed a special drop- 

 ping can to deliver the proper amount, so that extermination of craw- 

 fish from land is now quickly accomplished with slight labor or 

 expense. Crawfish are also excellent food for poultry. 



The female crawfish, distinguished from the male by her broader 

 abdomen, carries the eggs attached to her swimmerets, as do the lob- 

 sters and crabs (Fig. 136), the young passing through the nauplius, or 

 free-swimming, stage within the shell. Even after hatching, as tiny 

 crawfish they remain attached to the mother until after the third 

 molt, when they scatter to take care of themselves. 



One or two pairs, kept in an aquarium or vivarium during the 

 hatching period (March to June), will afford most valuable opportu- 

 nities for observing the instincts and habits of a crustacean. Per- 

 haps some member of the class will volunteer to do this. If so, he 

 must study carefully to make conditions as normal as possible, and 

 must feed well, or they may kill and eat each other, and the females 

 may even devour their own eggs. 



