36 HOMOPTERA 



the abdomen. The head is vety large, out of all proportion to the body, and the legs are feeble, 

 The eyes are likely to be prominent, and the ocelli and antennse absent or not distinguishable. 

 If the species is a pubescent one, the hairs are usually not developed in this instar. No vving pads are 

 visible and the abdomen is attenuated. The pronotum is not developed and the prothorax is about 

 equal in size to the other thoracic segments. 



In the second instar the size is usually doubled and the entire insect is much darker in appear- 

 ance. The prothorax is inclined to be swollen dorsally but no distinguishing protuberance of the 

 pronotum is apparent. No wing pads are visible. The head is more normal in comparative size and 

 the eyes not so prominent. The ocelli may now be distinguished and likewise the antennae. The 

 spines are still very complex and branched hvrt. seldom appear on the head. The anal segment of the 

 abdomen is prolonged and the entire body is stouter. 



In the thii-d instar the characteristic enlargement of the pronotum begins to appear and the 

 wing pads are evident. The prothorax is much larger than the other two thoracic segments. The 

 head is normal in size and the eyes are not over-prominent. The antennsE are plainly to be seen. 

 The spines have lost much of their complexity and are much shorter and less branched. In this stage 

 the spines of the head and thorax are often entirely wanting and the whole body develops pubescence. 

 The anal segment of the abdomen is still much enlarged and the anal tube is prominent. 



In the fourth instar the pronotal enlargement is pronounced, the posterior process usually covers 

 the mesothorax and the structures begin to suggest those of the adult. The wing pads are large and well 

 developed, usually extending ])osterioriy as far as the third abdominal segment. The head is reduced 

 in comparative size, the ocelli are larger and the antennae are normal. The spines are much reduced 

 in complexity if not in size; often they appear as mere stubs or bristles, and they are seldom seen on 

 any other part of the body than the abdomen. The insect has increased much in size and often 

 shows colors chaiacteristic of the imago. 



The fifth and last instar is the longest in duration and in this instar the nymph attains a size 

 comparable to that of the adult. The pronotal developments are very pronounced and the wing pads 

 are fully formed, usually reaching the fourth abdominal seginent. The spines are heavy but generally 

 rather simple. The head is much deflexed, and the eyes, ocelii and antennjE are normal. The beak 

 is fully developed, generally extending posteriorly as far as the hind coxse. The legs are strong and 

 stout and the abdomen is swollen. The anal tube is less prominent than in the preceding stages. 



The foregoing descriptions of the nymphal stages apply in general to the family as a whole and 

 of course there are many variations in different genera and species, but it is believed that these general 

 characters are sufficient to enable one to distinguish the various instars in most species. We believe 

 that the spines, which are very characteristic and constant, the development of the pronotum, the 

 appearance of ocelli and antennse, and the relative size of the wing pads, are good structural characters 

 fo diagnosis. 



The time required for each nymphal instar varies not only with the different species, but also 

 for the nymphs of a single species, and even for the individuals in a single egg mass. Consequently 

 only a very general statement can be made on this subject. Studies of North American forms indicate 

 that, very roughly, the average for each of the first four instars is about five days, and for the fifth instar 

 ten days, making a total of thirty days for the complete period of development from egg to adult, but 

 we have no data on the tropical forms in this respect, so that the above figures may not at all represent 

 the family as a whole. 



Thereare various typesof 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 



