Biology of the Membracidae of the Cayuga Lake Basin 379 



The variation between the periods of development of the different 

 species is probably normal and more or less indicative of the requirements 

 for each species concerned. 



The variation in one species in different years can probably be explained 

 by climatic conditions, and the same factor may explain the varying 

 periods required for different broods in the same season and even for 

 nymphs from different egg masses hatching at about but not exactly the 

 same time. 



The variation in the length of time required for nymphs from a single 

 egg mass is, however, not to be explained on this ground, and yet such 

 variation is very common. The factors entering into the problem are 

 rather numerous. When it is said that all the nymphs from one egg mass 

 do not reach maturity at the same time, it must be remembered that all 

 the eggs from this egg mass may not have hatched at the same time. It 

 has been shown, however, that the nymphs from the eggs first hatched do 

 not always reach maturity before those from the eggs last hatched. More- 

 over, the nymphs from eggs hatching at the same time do not reach 

 maturity together. Still further, nymphs that have hatched at the 

 same time and reached maturity at the same time have often not kept 

 together during the different molts. For example, the records of two 

 nymphs emerging on the same day showed respectively for the five instars 

 8-7-7-10-15 and 7-8-8-8-16 days, and transformed into adults on the 

 same afternoon. Such variation can be explained only by individual 

 and physiological differences not evident in the ordinary life-history 

 studies. There is often a difference of as much as two weeks between 

 the dates of maturing of the earliest and the latest individuals from the 

 same egg mass, and as much as one week between individuals from eggs 

 hatching on the same day. 



ECDYSIS 



There are various types of ecdysis, but seldom is there any variation 

 in this respect within a genus. In most cases the nymph of the last instar 

 fastens itself securely to the underside of a leaf just before its final molt, 

 and the old exuviae may be found in this position for several days after 

 the process has been completed. In some cases only the first pair of 

 legs are thus attached, in others all six legs. Some species do not attach 

 themselves and the old skin falls to the ground as soon as ecdysis is com- 



