RELATIONSHIPS OF THE COLLEMBOLA. 



The peculiar interest centering in the Collembola .is due 

 largely to the fact of their association with the Order Thysanura, 

 which contains the Campodea, an insect supposed by many to 

 represent pretty nearly the ancestry from which the Pterygota 

 have evolved. Whether the Pterygota did actually come from a 

 Campodea-like form, we do not know ; one thing is evident, how- 

 ever : if they did, the line of descent was not by way of the Col- 

 lembola. As to the connection between the two orders of the 

 Apterygogenea, various opinions exist. Some writers see no 

 connection at all, others would place them in the same order. I 

 believe that the differences are marked enough to justify the 

 separation into the two orders, though the evidence seems con- 

 vincing that the order Thysanura is the older of the two, and is 

 perhaps not far out of the direct line of descent from a common 

 ancestor. 



While I confess myself unable to point out the ancestor 

 of the Collembola among the members of the order Thysanura, 

 yet I feel pretty certain that such an ancestor must have 

 closely resembled members of the genus Machilis in many im- 

 portant respects. Machilis is not the ancestor, but there is no 

 other form known which possesses organs comparable with the 

 characteristic organs of the Collembola: the furcula, the ten- 

 aculum and the ventral tube. Scales are also found on tin- 

 Machilis as on several genera of the Collembola. It is interest- 

 ing to note even in this connection that the Machilis shows a very 

 primitive, even pre-hexapod, character in the possession of 

 biramous appendages. That the Collembola are scions of a very 

 old house seems probable, yet their minute size and their com- 

 paratively soft bodies make it equally probable that geological 

 rock-writings have but meager records to offer us concerning 

 them. As is so often the case, science must speculate, more 



