312 



ORTHOPTERA 



Acridiidse, from which tliey can be readily distinguished by the 

 characters we have mentioned in our definition. According to 

 Dufour, there are no air vesicles connected with the tracheal 

 system in this family ; possibly to this it may be due that none 

 of the family undertake the long flights and migratory wanderings 

 that have made some of the Acridiidae so notorious. Very little 

 is known as to the life histories of the members of this extensive 

 family of Orthoptera. Graber, however, has given some particulars 

 as to the development of Platydeis grisea, and of one or two other 



mt 



Fig. 188. Development of wings in Platydeis grisea: A, B, C, D, E, consecutive 

 stages ; p, prothorax ; vi, niesothorax ; vit, metathorax ; t, tegnien ; w, wing ; 

 ah', position of first abdominal segment. In C, D, and E, m points to the part by 

 Avhich the m, shown in A and B, is concealed ; ia D and E only the i)ositions of mt 

 are indicated. (After Graber.) 



species. He recognises five instars, but his first is probably 

 really the second, as he did not observe the Insect in its youngest 

 condition. Although his figures are very poor, we reproduce 

 them, as they give some idea of the mode of growth of the wings, 

 and of the correlative changes in the thoracic segments. It 

 will be seen that in the first three of these instars the alar organs 

 appear merely as prolongations of the sides of the posterior two 

 thoracic rings, and that in D a great change has occurred in the 

 position of these segments, so that the alar organs are free 

 processes, the two posterior thoracic rings being insignificant in 

 size in comparison with the now greatly developed prothorax. 

 In E the tegmen is shown fully developed, the positions of some 



