FAM. MEMBRACIDyE 35 



four or five egg inasses may be deposited by one female in a single day but after that she remains 

 quiescent for at least twenty-four hours, and very probably for several days, before another egg-laying 

 period begins. The number of eggs in one egg mass does not vary greatly for any one species and 

 shows an average of four for all the species studied by the writer, with a minimum of one and a maxi- 

 mum of thirteen. The most usual method of placing the eggs seems to be in a palmate arrangement 

 with the bases close together and the tips projecting outward, but in some species the eggs are laid 

 singly, in others in straight rows, and in still others in irregular clusters. 



The eggs are generally white or pearly, club-shaped or tooth-shaped, and about i.5 milUmeters 

 long by 0.3 millimeters wide at the maximum diameter. The egg may be smooth or sculptured, the 

 base usually being rounded and the tip pointed. In the eggs of most species a distinct neck is visible, 

 often grooved. The chorion is usually vitreous. The micropyle in most cases is oval, opening tan- 

 gential to the longitudinal axis. The cap is comparatively large, and before hatching becomes swollen 

 and wrinkled. The lateral margins of the egg are curved, one side often being more convex than the 

 other. Just before the eggs hatch they become slightly larger. 



Observations in the field and breeding experiments in the laboratory indicate that the average 

 duration of the egg stage for North American forms is approximately twenty days and for tropical 

 species about twelve days. We have one record of an incubation which lasted only four days. How- 

 ever, ecological studies have shown that climatic conditions have a decided influence on the incubation 

 of the egg and the development of the nymph so it is evident that there is much variation in the time 

 required for the hatching of eggs. The hatching is retarded by dry weather and accelerated by abun- 

 dance of moisture; likewise hatching is slower in cold weather than in warm weather. This may be 

 due, however, to the condition of the vegetation during favorable and unfavorable growing seasons and 

 it is possible that the ecological relationship between the insects and their hosts may have much to do 

 with variations in life histories, However, even in the same egg mass the eggs do not all hatch at the 

 same time, a difTerence of nearly a week between the first and the last having been observed in some 

 instances. 



The mechanics of the process of hatching is practically the same for all species studied. A few 

 days before hatching, the egg appears somewhat swollen. This is followed b}' the cracking of the 

 chorion about the neck and the upper end. Some days may elapse after the first splitting of the egg 

 before the insect emerges. Finally the cap is forced upward and the head of the nymph appears. 

 The head is quickly followed by the thorax and part of the abdomen. The nymph then appears to 

 rest for a few minutes after which the legs are slowly withdrawn in order, beginning with the first pair. 

 At the same time, the dorsal spines become protruded, while the insect is still held by the posterior 

 end of the abdomen inside the shell. Finally this posterior end of the abdomen is puUed out, 

 and the nymph creeps a very short distance away from the old shell and again rests The entire time 

 required for the emergence, from the time the head is first seen until the process is completed, is 

 usually about half an hour. 



AU of the species of Membracidte which the writer has studied show five nymphal instars. Each 

 of these five instars is usually distinct enough to be recognized, and displays characters sufficient not 

 only for the recognition of the species but also for the identification of the particular stage of develop- 

 ment that it represents. 



In the first instar the nymph is of course very small, not greatly exceeding in length the egg 

 from which it hatched, very light-colored, and extremely soft-bodied. Most nymphs have character- 

 istic dorsal spines on the thorax and abdomen. In the first stage these spines are much inclined to be 

 complex and branched, and are numerous on the head and thorax with often one or more rows on 



