10 COLLEMBOLA OF MINNESOTA 



or less futilcly, upon the line of descent which brought forth 

 the Collembola. That they are degenerates, retrograded from 

 an early pterygote stock, as some very good scientists have 

 guessed, seems to me a position more and more untenable the 

 better we become acquainted with these insects. 



Let us glance, in passing, at some of the evidence. There 

 are no wings, even vestigial, to be found in any members of 

 the group ; and even embryological research fails to reveal 

 any wing traces. This fact, while important, should not be over- 

 strained. It is merely a negative character possessed in common 

 with the Pediculidae and others which we have good reason 

 to believe have evolved from various winged orders. The 

 biramous, crustacean-like legs of Machilis, together with its 

 possession of a full set of small, jointed abdominal appendages ; 

 its campodiform body and simple mouth-parts and internal 

 structure ; all claim for it a place among very ancient insects. 

 The apposable claws of Collembola are more like the chelae 

 of crustaceans than like the claws of any others of the hexapods. 



Compound eyes were probably acquired, or possibly in- 

 herited, by the early hexapods ; and were possessed even by 

 those which failed to develop in a pterygote direction. The 

 ■collembolan eye is essentially a compound eye in process of 

 decadence. While most of the Thysanura are very simple and 

 rather sluggish insects, yet the Machilis has begun the devel- 

 opment of an organ which has become in the Collembola a very 

 important organ of locomotion — the furcula. If Collembola 

 were descended from pterygote insects, we would expect to find 

 among the latter some organ which we could conceive to have 

 ^specialized into the furcula. But such is not the case, though 

 Machilis does have the last pair of abdominal appendages larger 

 than the rest, and uses them together as a leaping organ. These 

 appendages are three-jointed, and the constant use of the pair 

 together as one organ would naturally tend to make their bases 

 approximate until they would grow together and form one piece, 

 the manubrium of the furcula in the Collembola. The two 

 more distal segments are free from each other. Probably none 

 of the appendages of the Machilis are used as a tenaculum ; 

 but all the appendages are there, and it is not surprising that 

 one pair should have been so modified, for the tenaculum is 



