BY R. J. TILLYAKD. 



187 



the latter, the forks are Af.3 and Af.4 respectively. Besides 

 this direct phylogenetic line, one or both of the forks may be 

 lost at any stage of the reduction, by suppression of a branch. 

 Thus, in the Leptoceridce, Oecetis (N. Zealand) keeps dc present 

 and Af.l sessile, but Af.2 is completely lost; while the allied 

 Triplectides (Australia) has progressed one stage further, having 

 Af 1 strongly stalked, 



(5) The thyridium-cell {tc) 

 is present in Hydropsyche 

 and Trias sopsyche, absent in 

 Mesopsyche. If, however, 

 the latter had a single cross- 

 vein from M3_|.4 to Cuj, its 

 tc would closely resemble 

 that of Hydropsyche in shape 

 and position. 



(6) The excess cells of 

 Mesopsychidce : here the 

 Mesop.sychidce o£fer a con- 

 trast, not only with the 

 Hydropsy chiiue, but with all 

 recent Trichoptera. In the 

 marine caddis-fly, Philauisus 

 plebejus Walker (Australia 

 and N. Zealand), there is a 

 small subdiscoidal cell which 

 may be comparable with the large sdc of Mesopsychidce; but, in 

 nearly all recent genera, there is nothing comparable with it. 

 The three post-discoidal cells (pdc) of Mesopsyche, the post- 

 median cell (pmc) of Triassopsyche, and the complicated cell- 



" Phylogeny of a principal cell in the wings of Triehoptei'a. A, oldest 

 stage, with both end-forks sessile upon the cell. B-C, successive reduction- 

 stages towards D, the csenogenetic stage, with both end-forks stalked. 

 At any stage, the cross-vein completing the cell distally may be lost, or 

 one of the forks may be reduced to a simple vein. — c, the cell; r, the main 

 vein, t'i+2' ^'3-1-4' ^^^ branches enclosing the cell basally; i\, Vo, the branches 

 enclosing the upper fork,/; v^, v^, the branches enclosing the lower fork, 

 /'; (c represents either dc or mc; v, either Rs or M). 



Text-fig. 5." 



