ANTJRIDA. 383 



converge towards one another to be inserted into the body- 

 wall on either side {ret. muse, in figs. 21, 23 and 36). By 

 means of the contraction of these muscles the distal lobes 

 are capable of being withdrawn into the basal column 

 when the organ is not in use. 



The cavity of the ventral tube is in direct communica- 

 tion with the general body-cavity of the animal, and 

 contains numerous blood corpuscles (b.c. in fig. 21), and 

 it is by means of the pressure exerted by the blood that 

 the protrusion of the vesicles is effected. When the organ 

 is in a retracted state its cavity is shut off from that of the 

 body of the animal by the contraction of the longitudinal 

 sternal muscles, which are disposed in two bundles 

 situated slightly to the outside of the organ on either side 

 (I. s. m. in fig. 38). The effect of the contraction of the 

 muscles is to approximate its anterior and posterior walls. 

 When the full expansion of the organ is desired both its 

 retractor muscles and the longitudinal sternal muscles are 

 relaxed. The slackening of the latter set of muscles 

 results in a sudden flow of blood into its cavity, and in 

 virtue of the turgidity thus acquired its terminal vesicles 

 are protruded to their fullest extent. 



With regard to the function of the ventral tube, 

 there has been, and is still, a great diversity of opinion. 

 Almost all investigators who have given any attention to 

 the structure of the Collembola have made suggestions 

 concerning it, and some of the views which have been put 

 forward appear to rest on a very slender basis. By 

 Kolenati (67) and Latreille* the ventral tube was 

 believed to be the external generative organ, and Claypole 

 (31) suggests the possibility of it being the relic of a 

 former outlet of the reproductive organs. Burmeistert 



* Nouv. Ann. d'Hist. Nat., t. 1, 1832. 

 f Handbuch dcr Entomologie, 1838, 



