436 



NEUROPTERA 



maim/ who agrees with Creutzberg ^ that the organ by which the 

 blood is propelled into the setae is a terminal chamber of the 

 dorsal vessel ; Yerlooren,^ who first observed this accessory system 

 of circulation, thought the contractile chamber was quite separate 

 from the heart. The nature of the connexion between this 

 terminal chamber that drives the blood backwards and the 

 other chambers that propel the fluid forwards appears still to 

 want elucidation. 



The nymphs of the Ephemeridae being creatures adapted for 



existence in water, the details 

 of their transformation into 

 creatures having an entirely 

 aerial existence cannot but be 

 of much interest. In the 

 nymphs the tracheal system is 

 well developed, but differs from 

 that of air-breathing Insects 

 in the total absence of any 

 spiracles. Palmen has inves- 

 tigated this subject,* and finds 

 that the main longitudinal 

 tracheal trunks of the body of 

 the nymph are not connected 

 with the skin of the body by 

 tracheae, but are attached 

 thereto by ten pairs of slender 

 strings extending between the 

 ^"'- If -^^ ^''™i*-f ^P'"""":'""' ';'.«;■'« chitinous integument and the 



■\vith gills ot left wide removed ; </, gills : ° 



B, nymph of Tricorythus sp. with gill tracheal truuks. 

 cover of right side removed ; gx, gill cover 

 ij, g'i gills. {After Vayssiere.) 



the 



When 

 skin is shed these strings — or 

 rather a chitinous axis in each 

 one — are drawn out of the body, and bring with them the chitinous 

 linings of the tracheae. Thus notwithstanding the absence of spir- 

 acles, the body wall is at each moult pierced by openings that 

 extend to the tracheae. After the ordinary moults these orifices close 

 immediately, but at the change to the winged state they remain open 

 and form the spiracles. At the same time the tracheal gills are com- 



1 Zeitschr. vnss. Zool. xxxiv. 1880, p. 404. 



2 Ann. Nat. Hist. (5) xv. 1885, j.. 494. ' Mem. Com: Ac. Bclg. 4to, xix. 1847, p. 1. 



■* Ziir Morpholoyie dcs Tracheensystems, Helsingfors, 1877, pp. 1-20. 



