_Papilio cresphontes._ | | 17. _Papilio asterias._ In second stage. | | 18. _Papilio troilus._ | | 19. _Papilio troilus._ In third stage; plain. | | 20. _Papilio philenor._ | | 21. _Papilio philenor._ In third stage; dorsal view. | | 22. _Papilio troilus._ In third stage; dorsal view. | | 23. _Achalarus lycidas._ Dorsal view. | | 24. _Papilio asterias._ In fourth stage; dorsal view. | | 25. _Thorybes pylades._ | | 26. _Papilio turnus._ Dorsal view. | | 27. _Papilio asterias._ | | 28. _Papilio turnus._ | | 29. _Thorybes pylades._ | | 30. _Epargyreus tityrus._ | | 31. _Epargyreus tityrus._ | | 32. _Thorybes bathyllus._ | | 33. _Epargyreus tityrus._ | | 34. _Eudamus proteus._ | | 35. _Epargyreus tityrus._ In third stage. | | | | [Illustration PLATE II.] | +--------------------------------------------------------------+ [Illustration FIG. 15.--Head of caterpillar of _Anosia plexippus_, side view, showing ocelli.] [Illustration FIG 16.--Caterpillar of _Anosia plexippus_, milkweed butterfly (Riley).] The body of the caterpillar is covered by a thin skin, which often lies in wrinkled folds, admitting of great freedom of motion. The body is composed, as we have seen, of rings, or segments, the first three of which, back of the head, correspond to the thorax of the perfect insect, and the last nine to the abdomen of the butterfly. On each ring, with the exception of the second, the third, and the last, there is found on either side a small oval opening known as a spiracle, through which the creature breathes. As a rule, the spiracles of the first and eleventh rings are larger in size than the others. [Illustration FIG. 17.--Fore leg of caterpillar of _Vanessa antiopa_, enlarged.] [Illustration FIG. 18.--Anterior segments of caterpillar of milkweed butterfly, showing thoracic or true legs (Riley).] [Illustration FIG. 19.--Proleg of caterpillar of _Vanessa antiopa_, enlarged.]