GENERAL ZOOLOGICAL FACTS AND THEORIES 



FIG. 161. The larval stages of a parasite, Sacculin a carcina. A, Nauplius; 

 B, Cypris; C, Cypris attached to host ; D, E, F, stages in degeneration 

 due to parasitic habit. (From Sedgwick after Delage.) 



The life history of the crustacean, Sacculina carcim, a parasite 

 on another crustacean, the crab, Car emus maenas, may be con- 

 sidered a good illustration of the degeneration of parasites. 

 Sacculina hatches as a Nauplius (Fig. 161, A), which soon changes 

 to the Cypris stage (B). After swimming about for two or three 

 days, the larva attaches itself to the setae of a crab by means of its 

 antennae (i). The base of the seta is penetrated by the hollow 



