64S E. N. PAVLOVSKY 



of the body, draws in the end of the body and swiftly pulls 

 it out again, as if trying to tear off something closing its 

 breathing apertures. Probably such movements are made 

 by the larva also under natural conditions after moulting, in 

 order to throw off parts of the old skin or the chitinous lining 

 of the tracheae, which might l)e left sticking to the hind end of 

 the body and thus diminish the breathing aperture or even 

 altogether shut it. 



After fifteen to tw^enty minutes the periods of movement of 

 the larva alternate with periods of rest. The movements of the 

 legs and the mouth-parts become convulsive, and are repeated 

 more and more rarely. I'lie larva rises passively and lies 

 under the surface of the glass in a bent attitude with its belly 

 up. In this case the significance of the tracheae as a natatory 

 apparatus is manifested l)est. The immovable larva is 

 not yet dead and can regain life if transferred into an 

 open vial ; the time during which a larva can be kept without 

 fatal results without air varit^s and de])ends on various circum- 

 stances, as temperature, individual peculiarities of the larva, 

 &c. In some of my experiments the larvae came to life again 

 after having been deprived of air for two and even seven hours. 



The question arises whether the pleural a})pendages (Text- 

 fig. 14) of the body and the caudal appendages play an accessory 

 part of tracheal gills, but I have not been able to clear this up 

 for want of material and other reasons. 



In conclusion of these remarks on the respiratory organs 

 we might discuss the finer structure of the tracheal trunks of 

 H. caraboides. As in all insects the chitinous lining (in- 

 tima) of its tracheae bears filiform thickenings, the t a eni d ia , 

 the windings of which give the tracheae a transversely striated 

 aspect. In the larva of H. caraboides the taenidia have 

 not necessarily the aspect of a spiral thread, as in some places 

 there are free ends of them between two adjacent windings ; 

 thus presenting a picture of structure similar to that observed 

 by Minot (1879) in Hydrophilus (Hydrous) piceus 

 (cited after Berlese, 1909). 



The degree of independence, or rather of precision, of the 



