BRANCH ARTHROPODA; CLASS IN SECT A : CHE INSECTS *77 



by their possession of an acrid body-fluid. The species 

 is thus protected against the most dangerous enemies of 

 butterflies, a fact which chiefly accounts for the great 

 abundance and wide distribution of the monarch (see 

 p. 137). For a full account of the life-history of the 

 monarch butterfly, see "Scudder's Life of a Butterfly." 



LARVA OF MONARCH BUTTERFLY (Anosia plexippus) 



TECHNICAL NOTE. For directions for finding and identifying the 

 larvae of the monarch butterfly see p. 171. If larvae (caterpillars) of 

 Anosia cannot be found, those of any other butterfly or moth will 

 do. Use naked, smooth kinds like cutworms, cabbage worms and 

 the like, rather than hairy or spiny ones. Use large specimens. 

 Kill the caterpillar with ether or in a cyanide bottle. 



Structure (fig. 44). As we have learned from the study 

 of the life-history of the locust, water-beetle and butterfly, 

 some insects are hatched from the egg in a condition 

 resembling that of the parents in most structural charac- 

 ters. This is true of the locust. Other insects, as the 

 beetle and butterfly, are hatched in a form and condition 

 apparently very different from that of the parents. The 

 external appearance of a beetle or butterfly larva differs 

 much from that of the adult or imago of the same indi- 

 vidual. It will be of interest to examine more particu- 

 larly the structural condition of one of these larvae and to 

 compare it with the structure of the adult. 



Is the body segmented ? Is the body composed of 

 head, thorax and abdomen? Note the soft, flexible, 

 weakly-chitinized condition of the body-wall. How many 

 pairs of legs are there ? Where are they situated ? Is 

 there any difference in the various legs ? If so, what is 

 the difference ? Which of the legs of the larva correspond 

 with the legs of the butterfly ? Why ? The prothoracic 

 segment and the abdominal segments I to 8 each bear a 

 pair of spiracles (small blackish spots on the sides). Are 

 both compound and simple eyes present ? How many eyes 



