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ESSENTIALS OF ZOOLOGY 



elements of. nature is during the egg stage, when it may remain 

 potent for months or even years if it falls in an environment unsuit- 

 able for development. 



External Anatomy 



This is one of the largest nematodes, females commonly reaching 

 a length of from eight to fourteen inches and males averaging six 



Fig. 123. — External anatomy of Ascaris lumhricoides, male and female. 



to twelve inches. Males are always more slender and have a curled 

 tail instead of the blunt tail of the female. The mouth is guarded 

 by three lips, two in lateroventral positions and one dorsal. These 



