672 



SCIENCE. 



[N. S. Vol. V. No. 122. 



rapid and enormous numbers existed. The 

 first important differentiation occurred in 

 the mouth structure long before wings be- 

 came developed, tending on the one hand to 

 a perfection of all or most of the parts, or 

 to a mandibulate type ; on the other to a 

 loss of certain of the structures, accompanied 

 by a different development of the others, 

 forming a haustellate type. In this latter 

 branch the mandibles were never developed, 

 the maxillary structures became elongated, 

 separated into their parallel parts, and the 

 labium became obsolete as a functional or- 

 gan. Just how many intervening orders ex- 

 isted between Tliysanura emandibulata and the 

 best development of the haustellate struc- 

 tures it is impossible to say ; but the only one 

 in existence at the present time is Thysanop- 

 tera, also called P?iysopoda, otherwise Thrips. 



This order I consider a distinct one on 

 the same branch from which arose the 

 Hemiptera, but forming merely a short spur 

 and retaining characters which were soon 

 lost in the main and more vigorous branch. 

 It is a survival which has lost the power of 

 further development, and can do no more 

 than merely maintain itself. The main 

 branch formed the Hemiptera, or, as I prefer 

 to call them, the Rhyngota, of to-day; the 

 mandibulate parts being completely lost, 

 the labium losing all external appendages, 

 and the maxillae forming the jointed beak 

 with its inclosed lancets. 



The Thysanoptera and Rhyngota of all the 

 existing orders are the only ones that do 

 not have functional mandibles in some stage 

 of their development. They are haustellate 

 from their birth, and the character of the 

 mouth parts never changes. In all the 

 other orders, either larv£e or adults, or 

 both, are mandibulate. I am aware that 

 there are seeming exceptions in several 

 orders, notably the Diptera; but it will 

 hardly be disputed that this order is of a 

 mandibulate stock, and many larvse have 

 the parts well developed. 



It results from the views just stated that 

 the Thysanoptera and Rhyngota are a division 

 equal in value to all the other, or mandibu- 

 late, orders combined. They have their 

 origin from the common stock ; but were 

 always haustellate or emandibulate in all 

 stages, forming the first and lower of my 

 main divisions. With the development of 

 this branch, after its distinctive feature be- 

 came established, I have nothing to do at 

 present. It seemed adapted for variation 

 in special lines only, and, as the method of 

 feeding was practicallj' fixed from the be- 

 ginning, there is a remarkable similarity in 

 mouth parts throughout. 



The mandibulata possessed much greater 

 powers of variation and a mouth structure 

 in which all the parts were developed and 

 capable of modification, containing possi- 

 bilities of much greater range in obtaining 

 food. They lived, therefore, under all sorts 

 of conditions, in all sorts of media, and all 

 kinds of modification were produced ; some 

 of them short-lived, adapted only to sur- 

 roundings then existing ; others with greater 

 possibilities, that exist to the present time. 



The first mandibulate insect had the 

 thoracic segments similarly developed, all 

 of about the same size and each of them 

 free ; but the advent of wings gave oppor- 

 tunity for radical divisions. I have no de- 

 sire to go into details here more than neces- 

 sary to explain my views of classification, 

 hence will not pretend to account for the 

 origin or development of wings. They did 

 appear, however, and independently at sev- 

 eral different points. In all cases the 

 wings were net-veined or neuropterous in 

 type, a peculiarity which is explicable if the 

 venation be considered of a tracheal origin. 

 With the appearance of wings many diver- 

 gences in habit were made possible and 

 new types began to appear. Three main 

 lines branched almost simultaneously from 

 the common stock, each of them fairly well 

 marked from the beginning, retaining its 



