COLLEMBOLA OF MaNNESOTA 7 



credence to the opinion, sometimes still advanced, that these two 

 segments have attained their super-growth to give more room 

 for the attachment of wing muscles, but inasmuch as the first 

 pair of legs are, as a rule the smallest, I think the other ex- 

 planation not only far-fetched, but unnecessary. 



The legs are five-jointed ; consisting, usually, of two short 

 basal segments, coxa and trochanter, a long femur and a still 

 longer tibia, with a very small tarsus, which bears, in all but 

 the lowest genera, two apposable claws, an outer larger, and 

 an inner smaller one. Clubbed hairs, the tenent hairs of many 

 authors, very often project from the end of the tibia over the 

 outer claw. The name "tenent" hair came from the notion that 

 they assisted the claw in grasping, or getting a foothold ; yet 

 I think there is little doubt that they are merely tactile in func- 

 tion. The claws often bear notches or teeth (denticles) espec- 

 ially along their inner edges, and the kind and distribution of 

 these present valuable systematic characters. In some of the 

 lower genera, as, for instance, in Achorutes, the inner claw is 

 disappearing, while in Podura and in most of the Aphoruridse 

 it is gone altogether. 



ABDOMEN. — This part is usually more or less swollen, 

 and consists of six segments, of which the apical and pre-apical 

 are usually small. The first abdominal segment bears on its 

 ventral surface the so-called ventral tube. This is the typical 

 organ of the Collembola, and one which all possess. True, 

 there is a wide difiference in appearance between the ventral tube 

 in Papirius on the one hand, with its long stock and two very 

 long, slender, flexible, tuberculated filaments, and that of Achor- 

 utes or Neanura on the other hand, where the tube is hardly 

 more than a tubercle split in the middle so that the two sides 

 shut together like the jaws of a steel trap, and the exsertile part 

 is only so far exsertile as to produce a convex surface when the 

 jaws are open and a concave surface when they are closed. The 

 function of this ventral tube is not well understood. Formerly 

 it was supposed to be an external reproductive organ. Latre- 

 ille held this opinion, but Nicolet said he could not agree with 

 the former author, although he had been unable to discover any 

 sexual organs. He seems to think it an organ which, by its 



