BY R. J. TILLYARD. 437 



EXPLANATION OF PLATE XLVII. 



Reftrenct Letters. — h, oblique base of gill — hp, basal pad — 6,s, small 

 blood-space— cap, capillary— cw<, cuticle of gill — att', cuticle of body-wall, 

 showing several, outer, coloured layers, and an inner, clear (uncoloured) 

 layer— e;>, epithelial syncytium of gill— ep', epithelium of rectal wall — 

 es, secondary efferent trachea — hh, hypobranchial tissue — hy^ hypoderm — 

 in, intima of rectal wall — lam, gill-lamellse — nii^, nucleus of gp—m^jj nucleus 

 of bj)—pg, pigment granules — ta, anterior tubercle — tp, posterior tubercle 

 — tr, large trachea. 



Fig.l. — A single gill-lamella of H emicordulia tau Selys,( well-grown larva); 



(x95). 

 P'ig.3. — Three gill-lamellje of same, viewed in profile, to show the lamellar 



tubercles; ( x 95). 

 Fig. 3. — Section along the line xx (indicated by arrows) in Fig.l, to show 



the histology of the gill; ( x 400). 

 Fig. 4.— Section along the line yy (indicated by arrows) in Fig.l, to show 



region of large tracheae; ( x 400). 

 Fig.5. — A small part of the distal portion of Fig. 3, much enlarged, to show 



histology of the gill-lamella; ( x 2500). 

 Fig.6. — Comparison of (a) the body-wall, (6) the undifferentiated rectal 



wall, and (c) the gill-wall in dragonfly larvae; (all three x 750). 



