394 



NEUROPTERA. 



segments in the course of the development, differ from those 

 that occur in Orthoptera. 



There are several peculiarities connected with the wings. 



rrequently they exist, 



though of no use for 



some Psocidae that 



perfectly - formed 



Fig. 246. — Micropterous form of Mesopsocus uni- 

 punctains. a, a, Wings. (After Bertkau.) 



flight 

 have 



wings are so reliictant to 

 use them that, M'Lachlan 

 says, they will allow them- 

 selves to be crushed with- 

 out seeking to escape by 

 flight. At certain periods, however, some Psocidae float on 

 the wing in considerable numbers, especially in a moist still 

 atmosphere, and then drift about like the winged Aphididae, 

 which are frequently found with them. There is evidence 

 that individuals, or generations, of some of the winged species 

 occur with only rudimentary wings ; although this has been 

 denied by Kolbe, there can be no doubt about it. The form 

 figured above (Fig. 246) was described by Bertkau -"^ as a dis- 

 tinct genus, but was afterwards recognised by him ^ to be a 

 short-winged form of Ilrsopsocns unipundatus. It is probable 

 that the adult female of this species has the wings always 

 micropterous, while the male has these organs of the full size. 

 In other species the condition of the rudimentary wings seems to 

 be quite constant. The facts concerning the wings of Psocidae 

 are so peculiar that Kolbe came to the conclusion that the 

 organs exist not because they are of use for flight, so much as 

 because it is the nature of an Insect to develop wings.^ 



Some of the species of Psocidae have never any trace of wings. 

 These apterous forms are mostly included in the division 

 Atropinae, and are usually very minute ; it has been again and 

 again erroneously stated that they are the young state of winged 

 forms. Hagen kept a large colony of Atropos divinatoria for 

 some years in confinement, so that he saw numerous generations 

 as well as many specimens. He found the apterous condition 

 quite constant. 



1 Arch. f. Naturg. xlix. i. 1883, p. 99. 



^ Verli. Ver. Rheinland, xxxix. 1882, Corr.-bl. p. 128. 



' Berlin cnt. Zeit. xxviii. 1884, p. 36. 



