280 EEPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



form is gradually assumed througli a series of five molts, at the first four 

 of which the wing-pads become more and more apparent, and at the last 

 of which, from the pupa (Fig. 19, c) to the perfect state, the thorax be- 

 comes flattened, full wings are acquired, and the insect ceases to grow, 

 except as the female abdomen becomes gravid and heavy with eggs. 

 Yet with each molt, aside from the colo rational changes, certain minute 

 and less striking structural changes invariably take place, by observing 

 which we may always know the comparative age and the particular 

 stage of growth of any individual. These stages are well illustrated in 

 Plate I, and we will briefly indicate the more minute structural differ- 

 ences in each : 



Firs* stage (PL I, Fig. 1).— This, which may be called the first larval stage, is charac- 

 terized by the speckled gray coloring, the proportionally large head, and by the anten- 

 nae, which are short and thick, having from 12 to 13 joints, never more ; the last number 

 the most frequent, and joints 4, 5, 6, and last shorter than the others. The meso- and 

 metanotum are subequal in length and together nearly as long as the pronotum. Aver- 

 age length 4.3™™. 



Second stage (PL I, Fig. 2). — With the first molt, the general color darkens; the black 

 marks intensify and the face becomes pitchy-black. There is often a consiDicuous pale 

 stripe along the middle of the ridged back. The antennse are 16-jointed, the 6th, 7th, 

 8th, and 9th joints of the preceding stage dividing toward base. The pronotum ex- 

 tends more or less over the mesonotum, so as to be longer than this last and the 

 metanotum together, and the lower edges of these two are lull and rounded, giving the 

 first indication of wing-pads. This may be called the second larval stage. Average 

 length 6.8™™. 



Third stage (PL I, Fig. 3). — With the second molt we get the third larval stage, in 

 which the pale and dark colors still more strongly contrast and the face becomes still 

 more pitchy. The ]pronotum entirely covers the mesonotum and not unfrequently a 

 part of the metanotum ; while the lower edges of these are subacutely produced inta 

 true wing-pads, the front one bub slightly narrower than the hind one. The antennse 

 are still 16-jointed but with the joints more equal in length. This maybe termed the 

 third larval stage. Average length 9™™. 



Fourth stage (PL I, Fig. 4). — With the third molt the pronotum, instead of having a 

 straight transverse border, is much produced behind and now entirely covers and hides 

 the other notal joints. The wing-pads, instead of extending downward, are turned up, 

 so that their upper ends meet on the narrow back ; the hind pair triangular, with a pale 

 disc, and partly overlapping the front pair, which are narrower and longer but do not 

 extend so far; the bases of both being bidden by the pronotum. Antennoe with 19 or 

 20 subequal joints. Average length 14™™. This may be known as the firsfc pui^al stage. 



Fifth stage (PL I, Fig. 5). — With the fourth molt the pronotum is still more produced 

 behind, and the wing-pads, though retaining the same positions, are as long as the 

 pronotum, the front pair more hidden by the hind pair but extending nearly as far. 

 The antennsB have 22 joints. Average length 17™™. This is the true or second pupal 

 stage. 



Sixth stage (PL I, Fig. 6). — The perfect winged insect, defined in Chapter I. The an- 

 tennsB have from 23 to 26 joints, those of the $ generally one more than those of the ^ . 



European authors differ as to whether there are three, four, or five 

 molts in the European migratory species;^" but we have watched spre- 

 tus from the egg to the imago, and thousands of mounted and alcoholic 

 specimens of all ages show the stages enumerated. The transition from 

 the second to the third, however, is sometimes not very marked, and it 

 is not improbable that, as is the case with many other insects, the num- 

 ber of molts may vary according to the amount of nutrition and rapidity 

 of development. 



The sexual characters are not well marked, and the sexes are conse- 

 quently with difficulty distinguished, in the first three stages. In the 



fi" See Koppen, " Ueber die Heuschrecken in Siidrussland," 1862, pp. 22, 23. 



