76 THE CANADIAN ENTOMOLOGIST 



and is normally folded under the insect with the free forked end towards the 

 head. The dentes terminate in curious hooked and toothed pieces (the mucrones) 

 plainly designed to give the insect a firm purchase for its leap; and with the 

 same object in view, the underside of the dentes are often studded with spike- 

 like setae. The acme of stinginess is reputed to have been reached by a man 

 who used a wart on the back of his neck for a collar botton. Without accusing 

 the springtail of parsimony, it must be stated that it adopts much the same 

 means to hold its furcula in place. On the third abdominal segment is a curious 

 little double-fingered protuberance (the tenaculum) which, when the furcula is 

 folded in place, projects between the dentes. The fingers of this excrescence 

 each provided with three or four teeth to ensure a firm grasp — bending outwards 

 against the dentes, serve to hold the furcula close along the belly, where it is 

 under considerable tension from the muscles of the manubrium. When the 

 fingers of the tenaculum are relaxed, these muscles pull the furcula strongly 

 downwards and backwards, and the insect is flung upwards into the air. Any- 

 one who remembers that homely toy, the goose-bone jumping jack, that used to 

 delight the children of a past generation, will readily understand how a spring- 

 tail leaps. 



The length of a jump may be as much as five or six inches. An Achorutes 

 socialis, one millimeter long, easily springs four inches or 100 millimeters, and 

 A. socialis is by no means one of the most active species. In proportion to the 

 size of the insect, these are prodigious leaps. It is as if a man could cover a 

 mile in nine or ten bounds. 



While in the air, the insect folds the furcula back into place again, so that 



on alighting it is immediately ready for another leap, and it almost invariably 



comes down on its feet. Only a few species, however, such as Tomocerus 



flavescens, jump several times in quick succession. Generally there is an interval 



of half a minute or more between the leaps. And, as a rule, leaping is only 



resorted to in order to escape from danger. The usual mode of progression is 



walking or running by means of the legs; although the migrating kinds when on 



the march, keep leaping from time to time, but apparently largely at random. 



While the springing apparatus is the most noticeable structure of the 



majority of the Collembola, it is not the distinguishing mark of the Order, for, 



as already mentioned, a good many species are entirely without it. It is the 



possession of the mysterious organ known as the "ventral tube" that decides 



the springtail lineage. This organ, situated ventrally on the first abdominally 



segment, is in some species merely a cleft tubercle, the sides of which open 



back like the jaws of a steel trap, exposing a wet, stickly-looking disc within. 



In other species it takes the form of a relatively long, projecting tube, from 



which (among some of the Symphypleona) can be protruded two lengthy, 



slender, transparent filaments, thickly studded with circular glands. 



Dissection does little to explain the use of the organ, but Sir John Lubbock 

 named the order Collembola — literally "glue-insertion" — ^from the idea, com- 

 mon to most entomologists of his day and apparently still held by some writers, 

 that the ventral tube enabled "the creature to attach or glue itself to the body 

 on which it stands." That this is the special function of the organ seems very 

 doubtful. Springtails do not appear to be in any particular need of attaching 

 themselves so securely to surfaces. They do not habitually live upside down, 



