ORIGIN OP THE WINGS. 173 



Now we conceive that wings formed in much the same way, 

 and with no more disturbance, so to speak, to the insect's organ- 

 ization, appeared during a certain critical period in the meta- 

 morphosis of some early insect. As soon as this novel mode of 

 locomotion became established we can easily see how surround- 

 ing circumstances would favor their farther development until 

 the presence. of wings became universal. If space permitted us 

 to pursue this interesting subject farther, we could show how 

 invariably correlated in form and structure are the wings of 

 insects to the varied conditions by which they are surrounded, 

 and which we are forced to believe stand in the relation of cause 

 to effect. Again, why should the wings always appear on the 

 thorax and on the upper instead of the under side? As this is 

 the seat of the centre of gravity, it is evident that cosmical laws 

 as well as the more immediate laws of biology determine the 

 position and nature of the wings of an insect. 



Correlated with the presence of wings is the wonderful dif- 

 ferentiation of the crust, especially of the thorax, where each 

 segment consists of a number of distinct pieces ; while in the 

 spiders and Myriopods the segments are as simple as in the 

 abdominal segments of the winged insect. It is not difficult 

 here to trace a series leading up from the Poduras, in which the 

 segments are like those of spiders, to the wonderful complexity 

 of the parts in the thoracic segments of the Lepidoptera and 

 Hymenoptera. 



In his remarks "On the Origin of Insects,"* Sir John Lub- 

 bock says, "I feel great difficulty in conceiving by what natural 

 process an insect with a suctorial mouth like that of a gnat or 

 butterfly could be developed from a powerfully mandibulate type 

 like the Orthoptera, or even from the Neuroptera." Is it not 

 more difficult to account for the origin of the mouth-parts at 

 all? They are developed as tubercles or folds in the tegument, 

 and are homologous with the legs. Figure 186 shows that the 

 two sorts of limbs are at one time identical in form and relative 

 position. The thought suggests itself that these long, soft, fin- 

 ger-like appendages may have been derived from the tentacles 

 of the higher worms, but the grounds for this opinion are uncer- 

 tain. At any rate, the earliest form of limb must have been 

 that of a soft tubercle armed with one, or two, or many terminal 



• Reported la " Nature " for Nov. 9, 1S71. 



