336 THE INVERTEBRATA 



Stage becomes parasitic on the gills of a flat fish, deriving nourish- 

 ment from its host by means of suctorial mouth parts. Here it passes 

 into a "pupal" stage in which the power of movement is lost and 

 retrogressive changes have taken place. Presently it regains the 

 power of swimming and leaves the host in an adult copepod stage. 

 In this stage impregnation takes place. The male develops no further, 



Fig. 242. 



vas d. 



Fig. 241. 

 Fig. 241. ChoTidracanthus gibbosus. After Claus. A, Female. B, Male, more 

 highly magnified, al. alimentary canal; an/ antennule; a?i/' antenna; e. eye; 

 e.s. egg "sac"; mxp. maxilliped; t. testis; th.z and 3, thoracic limbs; vas d. 

 vas deferens ; cJ, males attached to female. 



Fig. 242. Stages in the life history of Lernaea. A, Metanauplius. B, First 

 Cyclops stage. C, "Pupa". D, Sexual stage: coition. E, Ripe female. 

 an/ antennule; an/' antenna; fix. secretion of a gland by which fixation is 

 effected ; hd.pr. processes of the head of the female which are imbedded in the 

 tissues of the host; mxp. maxilliped; sip. siphon; th.2, second thoracic limb; 

 rafn. ramus of caudal fork. 



but the female attaches herself to the gills of a fish of the cod family, 

 where by a great development of the genital somite she becomes con- 

 verted into a vermiform parasite, anchored into the host by processes 

 that grow out from her head, and retaining only the now relatively 

 minute appendages of the thorax. 



