SPRING-TAILS CHAP. 



of restraint by the catch, when the latter is removed the spring 

 extends by reason of its elasticity, and the leap is thus executed. 

 Whether this is really the exact method of leaping is, however, 

 doubtful, for Lubbock says that the catch " only exists in certain 

 genera " ; while in its structure it does not appear to be well 

 calculated to retain in position an organ that by virtue of its 

 elasticity is constantly exerting a considerable force. 



The ventral tube is an anomalous and enigmatic structure. 

 In the lower forms, such as Lipura or Anurida, it consists merely 

 of a papilla (Fig. 100, A, a) more or less divided by fissure into two 

 parts. In the Smynthuridae it is more highly developed, and 

 protects two long delicate tubes that are capable of being 

 protruded, as shown in the outline profile of Smynthurus fuscvs 

 (Fig. 99), which is taken from specimens preserved in balsam by 



Mr. J. J. Lister. The nature and use 

 of this ventral tube have given rise to 

 much discussion. Lubbock considered, 

 and others have agreed with him, that 

 it serves to attach the Insect to bodies 

 to which it may be desirable the Insect 

 should, when in the perpendicular posi- 

 tion, adhere. Eeuter x assigns a quite 

 different function to this singular struc- 



FIG. 99. Smynthurus fuscus, tura He gtates that the hairs of the 

 with exsertile vesicle (a) pro- 



truded from ventral tube; body are hygroscopic, and that the 

 b, the spring extended. peculiar claws of the Insect having 



collected the moisture from the hairs, the ventral tube becomes 

 the means, of introducing the liquid into the body. These Insects 

 possess, however, a mouth, and there seems to be no reason why 

 a complex apparatus should be required in addition to it for so 

 simple a purpose as the introduction of moisture to the interior of 

 the body. Haase finds 2 that Collembola can crawl 011 glass 

 without the aid of the ventral tube ; he considers its function 

 to be physiological, and that it may probably be respiratory as it 

 has been suggested is the case with the vesicles of Thysanura. 

 The function of the ventral tube is certainly not yet satisfac- 

 torily elucidated. The vesicles contained in it are said to be 

 extruded by blood-pressure, and withdrawn by muscular action 

 in a manner similar to that which we have described as occurring 

 1 Ent. Tidskr. i. 1880, p. 159. - Morplwl. Jahrl. xv. 1888, p. 3fil. 



