Occasional Papers of the Museum of Zoology 7 



recorded separately. The larvae of the first collection were 

 found to range from 16 to 128 millimeters in length and those 

 of the latter from 17 to 126 millimeters. The measurements 

 were plotted and used as the basis for the life cycle curves 

 shown in Figs, i and 2, for the two collections respectively. 

 The ordinates in the curves represent the number of indi- 

 viduals and the abcissae their lengths in millimeters. 



A study of these graphs reveals the fact that they are made 

 up of several distinct modes around which the larvae seem to 

 be grouped. This can scarcely be a matter of chance, since 

 both of the collections exhibit the same groups. The groups 

 undoubtedly represent different generations of larvae, and the 

 conclusion is reached that the length of the life cycle in this 

 form and in this particular locality is seven years. This does 

 not preclude the possibility, however, that some precocious 

 individuals may metamorphose at an earlier stage than others 

 and that some retarded individuals may even take more than 

 seven years for their full development. The great amount of 

 variation in the size of the larvae due to inequality of growth 

 makes it impossible to determine with any degree of exactness 

 the age of any single individual. The only part of the curve 

 that stands out definitely in each case is that part which rep- 

 resents the youngest larvae in the collection, namely, those 

 three months old. From this time on the year-group curves 

 merge more or less with one another and it is only possible 

 to arrange the larvae according to age around certain average 

 sizes. The full-grown larvae are grouped around the last 

 mode, which is at 105 millimeters, and although two trans- 

 formed individuals were found to be shorter than this, it is 

 likely that the adults would on the average be about 105 milli- 

 meters or more. Alost of the larvae grouped around the last 



