68 THE VENTRAL TUBE. 



and Lijpuridce, as well as in Podiira and Isotoma ; in 

 Orchesella, Tomocerus, Templetonia, BecJcia, Seira, Lepi- 

 docijrtus, and Degeeria, on tlie contrary, that of the 

 third or fourth abdominal segment is considerably 

 larger than the rest. 



M. JSTicolet describes four pairs of spiracles placed 

 on the superior arches of the four first segments of 

 the abdomen ; " ils occupent le milieu de chaque bord 

 lateral des segments ci-dessus mentionnes." Warned 

 by the material differences which, as we shall presently 

 see, exist in two groups otherwise so nearly allied as 

 8mynthurus and Papirius, I should not like to assert 

 that these spiracles do not exist at all, bnt I have not 

 been able to find them in any of the Poduridce which I 

 have dissected. 



Underneath the anterior abdominal segment is the 

 ventral tube, or sucker. In Podura, Lijmra, and the 

 allied genera, this organ is a simple tubercle ; divided 

 into two halves by a central slit ; in other genera, as, 

 for instance, in Orchesella and Tomocerus, the tubercle is 

 enlarged, and becomes a tube divided at the free end 

 into two lobes. In the Smynfhuridce and Papiriidce the 

 organ receives a still further and very remarkable 

 development ; from the end of the tube the animal can 

 project two long, delicate tubes, provided at their 

 extremity with numerous glands. 



This remarkable organ was supposed by Latreille to 

 be the external generative organ. Nicolet was right 

 in disputing this, and truly observes that the ventral 

 tube presents the same form and structure in all the 

 specimens of the species. He was unable, however, to 

 settle the case anatomically, being bafiled by the 

 minuteness of these little creatures. More fortunate 

 than he was, however, I shall presently describe the 

 generative organs, which, as Nicolet correctly antici- 

 pated, open at the posterior end of the abdomen ; and 

 also the true structure of the ventral life itself, which 

 is extremely curious. 



