O ME. D. J. SCOUHriELD ON ENTOMOSTEACA 



There is yet another point to be noticed in connection with, this 

 anterior series of setae. At some distance beyond the outer 

 branches an excessively faint marking may be seen (see PI. II. 

 fig. 2) running parallel to a line joining their tips, and consisting 

 of short closely-set lines. I believe this marking is really the 

 outer edge or fringe, so to speak, of a number of imbricated 

 hyaline scales supported by the setae. This is a point, however, 

 that has not been clearly demonstrated ; and the supposition is 

 based mainly upon comparison with the more evident scales found 

 in connection with the middle series of setse. 



In the middle series there is always a distinctly double row of 

 comparatively short and nearly straight setse, pointing approxi- 

 mately backward, the setse of the inner line inclining somewliat 

 inward, and those of the outer line outward. They are arranged 

 in pairs, of which there are about twenty ; and the bases of the 

 setae of each pair are joined by a faint ridge. "Where the setae of 

 the inner line project beyond the edge of the valve, they can be 

 seen to support a series of very delicate slightly overlapping 

 scales, the edges of which, under high magnification, have a similar 

 appearance to that noticed just beyond the tips of the setae of 

 the anterior series. A view of three of these scales is shown on 

 PI. II. fig. 3. Analogy would lead one to suppose that similar 

 scales would be found supported by the outer line of setae ; and 

 such is actually the case, but these cannot be so readily observed. 

 Probably also the scales of each pair of setae join in the middle, 

 although this has not hitherto been certainly proved. 



The posterior series usually comprises only two setae, pointing 

 backward, of which the anterior one is bifurcated and the 

 other simple. They are longer than those of the preceding 

 series, but give rise apparently to hyaline scales of identical 

 structure. 



Before leaving this subject of the modified ventral setae, it 

 must be stated that in the male there is only a single row down 

 the whole length of each valve. The setae are essentially the 

 same in their coarser structure ; but they seem to be simply 

 plumose instead of giving rise to hyaline scales. This appear- 

 ance may nevertheless be produced by a much greater fringing 

 of the edges of the scales than is the case in the female. If not, 

 these male setae evidently represent a stage in the evolution of 

 the more complicated structures already described. 



Prom the foregoing description, especially of the setae fringing 



