60 ILLINOIS BIOLOGICAL MONOGRAPHS |302 



but one-eighth, we naturally begin to doubt that this stadium represents 

 the same stages of development in these species. The data presented will 

 serve to illustrate this condition. We note that the time required to pass 

 various stadia relative to the total larval life varies considerably in species 

 and to some extent in individuals. The question arises as to how much of 

 this difference is due to external factors and what proportion of it is attrib- 

 utable to innate tendencies. The effects of change of temperature, of 

 starvation, and of parasitism upon individuals of PoHa renigera are very 

 marked, as is the influence of seasonal conditions upon different broods of 

 Coramica picta, demonstrating the pronounced effect of external factors 

 upon the length of stadia. The innate tendencies in this respect can be 

 determined accurately for various species only by rearing their larvae under 

 constant conditions, as has been done with Polia renigera and A gratis 

 ypsilon. These were reared at both 28 degrees C. and 21 degrees C. in 

 ventilated jars at 100% relative humidity. The individual variation in the 

 relative length of the stadia of the few individuals which were so reared we 

 cannot satisfactorily explain. Larvae of these two species reared outside do 

 not differ uniformly in the proportional length of their stadia from those 

 grown under constant conditions. 



The lack of data derived from rearing larvae in this manner precludes 

 our drawing definite conclusions as to the innate relations existing between 

 the duration of different stadia in different species. Nevertheless a com- 

 parison of species reared outside may offer us significant indications regard- 

 ing this point. It will be noted that the larvae of two species of tussock- 

 moths, Notolopha antiqua and Henierocampa leucostigma, which were reared 

 by Payne in Nova Scotia under natural conditions, present a relatively 

 long first stadium. Larvae hatching from forced hibernating eggs of the 

 latter species in Illinois and grown in a warm laboratory by the author 

 also required an unusually long period for passing this stadium, indicating 

 that this unusual condition is not to be explained by the effect of external 

 conditions upon the larvae. Nor is it correlated with hibernation in the 

 egg stage, since three species of larvae of Catocala hatching from hiber- 

 nating eggs about the same time failed to show this condition, the first and 

 second stadia requiring about an equal amount of time. In all noctuid 

 larvae reared by the author the last stage has been markedly the longest, 

 whereas in these two species of liparid larvae the last two stadia are nearly 

 equal in duration. The three larvae of Dipterygia scahriiiscula, showing the 

 long first stadium, hatched on the same day as the fifty-one individuals of 

 Agroiis ypsilon and were reared under the same conditions, yet all of the 

 latter species required approximately the same amount of time for passing 

 first, second, and third stages. In Polia renigera there seems to be a general 

 increase in the length of the two latter stadia, while only the last stage is 

 long in Agrotis ypsilon and Lycophotia margarilosa. These facts all indicate 



