80 



CAUDAL GILLS OP ZYGOPTEKID LARViE, 



prisms except that they become gradually enlarged towards the 

 tip, and finally taper to a rather blunt point. Their transverse 

 sections are everywhere triangular. The term ^HriquetraV is 

 frequently used to describe these gills, and seems to be the most 

 suitable term available. 



mr 



tf Tiv K'y cu 



Text-fig. 17. 

 Ideal (semi-diagrammatic) T.S. across the Triquetro-qviadrate Gill-system 

 of Galopteryx, to show the internal structure of the gills. Lettering 

 as on p. 109. 



The shorter median gill has all the appearances of a vertical 

 lamella, except that it is somewhat thickened. This gill also 

 increases in width towards the tip, and then tapers to a point. 

 The distal part of the gill appears to be curved over downwards, 

 giving it a somewhat "nodding" appearance. This curvature is 

 shown also in the blood-canals, which are also slightly down- 



