78 Cincinnati Society of Natural History. 



and the 4th, July dth. Each of these stages lasted eight da^-s ; but 

 the larva did not begin to spin its cocoon until Juh* 21st, so that the 

 last stage lasted about as long as an}- three of the previous stages. 

 Phyciodes tharos passes (Edwards states) 5 to 6 days in its 1st stage, 

 and the same in its 2d, three days in the 3d stage in summer, but 7 to 

 14 days in the fall, three to five days in the 4th stage, four to six daj s 

 in the 5th stage, and 6 to 13 days as pupa, unless "retarded by cold." 

 In Satyrus nephele the larva hibernates in the first stage, passes 23 

 days in its 2d stage in spring, 14 days each in its 3d and 4th stages, 

 and twice fourteen in the 5th, and 14 again as pupa. 



These instances might be multiplied indefinitely. They show an 

 approach to a regular period for the duration of each stage; and that 

 there is a regular ratio between the duration of the several stages. But 

 in all of these cases the larvae ma}- be called long lived; so that thej- 

 are exposed to cliange of seasons, and vicissitudes of temperature. 

 These larvse also feed externallj^ on vegetation. That food and tem- 

 perature do exercise an influence on growth and development every 

 body knows ; and, therefore, we see that larvte which are so much ex- 

 posed to changes of these influences, can not so well display- the 

 periodic character of their metamorphoses as larvae, which are shorter 

 lived, and therefore less exposed to be influenced b}^ changed conditions 

 of life. Besides these comparatively large larvae feeding externally, 

 and needing to haye their food constantly- renewed, can not be so well 

 supplied with appropriate nourishment as larvae, which pass more 

 rapidly through their changes, and live inside of leaves, where nature 

 has supplied them with an abundance of their appropriate food, and 

 which only require therefore to be confined in a moist chamber for a 

 few days without change of food or temperature. The leaf mining- 

 larvae are for these reasons better fitted for accurate observations of 

 this character than the larger larva? of Butterflies, and from observations 

 on them I arrive at conclusions which are indicated, but not, perhaps, 

 fully established by such cases as 1 have called your attention to. 

 These conclusions are that food and temperature remaining the same, 

 there is a fixed period in each species for the duration of each stage ; 

 that usually in each species all larval stages are of the same length ; 

 that an alteration of food or temperature, or both, usnall}' alters the 

 duration of each stage, but does not always do so; that is, that usually 

 a given amount of food, and a temperature, which is fixed for each 

 species, produces an amount of growth and development, which necessi- 

 tates, and in some wa}' produces, a shedding of the skin ; but that occa- 

 sionally^ another force manifests itself in overruling the eflect of food 



