332 



ANIMAL LIFE 



FIG. 375. Five larvae of a chalcis fly in a bunch on a caterpillar. Photograph 

 nearly twice life size. 



certain species parasitize the eggs of the harmful insects, 

 thus rendering great service. Tachina flies aid in the 

 good work also. Their minute eggs are 

 glued to the skin of the host separately 

 (Fig. 26). 



In cases where the young live an in- 

 dependent life and the adults are para- 

 sites, marked degeneration often occurs, 

 which is especially noticeable among the 

 crustaceans. Sacculina exhibits in youth 

 the characteristic features of its order, but 

 after becoming a parasite on the crab in 

 later life, the legs, eyes, and mouth parts are entirely lost 

 and it absorbs nourishment from its host by numerous del- 

 icate, rootlike suckers. Other peculiar crustaceans, known 



FIG. 370. -A Tachin 

 fly- Photograp 



slightly enlarged. 



