fiY R. .1. TILLYARD. 



105 



Viewed externally (Text-fig. 30), the gills are striking in theii* 

 shortness and stoutness; indeed, they do not, even at first sight, 

 at all suggest true caudal gills, but rather a somewhat enlarged 

 form of anal pyramid such as we find in the lar\a' of Anisoptera. 

 In actual shape, as revealed by cross-sections, they might be 

 classed as Triquetro^quadrate, or intermediate between this and 

 the Saccoid Type. The median gill is broadly diamond-shaped 

 in section, the laterals convexly tritpietral. This shape is evi- 

 dently brought about by the habit of resting the median gill 

 upon the laterals, and the laterals uj)on the I'esting-surface. The 

 larva is, to all intents and purposes, a ground-dweller, like those 

 of the CalojJteryyinw, but the "ground," in this case, is not the 

 river-bed, but the debris collected in the little leaf-jwols. The 

 return to the triquetro-quadrate outward form is, therefore, a 

 veiy interesting example of the efiect of change of habit on the 

 form of the gills. 



Text-fig. 81. 

 Ideal (scini-diagiaiiimatic) T.S. across the RediKjecl (non-fuiietional) Oill- 

 .sy.stein of A(jrloit aMtliti' Perkins, to show the internal structure of the 

 ^ills. Lettering as on p. 109. • 



Internally, these gills difier greatly from all others studied in 

 this paper. The cuticle is exceedingly thick, from 12-16/x, of 



