146 ELEMENTARY ZOOLOGY. 



The fleas are transient parasites, as are many other insects 

 which are free in the adult stage, but lay their eggs in 

 or on the body of the host, where they undergo a partial 

 development as parasites at the expense of the host 

 (Figs. 33, 34). In other instances the parasite has come 



I tor 



FIG. 34. A tomato worm bearing the cocoons of a parasitic insect. From Folsom's 

 Entomology. 



Questions on the Figure. Seek for all possible figures of cater- 

 pillars attacked by parasites. Why would caterpillars be rather 

 favorable hosts for insect parasites? Of what economic importance 

 are these facts? 



to spend its whole life in the body of one or more hosts. 

 These are called permanent parasites. 



It will be seen that the parasite increases the work to be 

 done by the host, thus becoming a handicap in the struggle 

 for existence. But since practically all animals support 

 various parasites the race is evened up. It is to the ad van- 



