Plate IV., Fig. 1, is the Shaft of a House Martin Contour feather. This 

 photograph has a magnification of 40 times. The object of this illustration is to 

 show the irregularity in the spacing of the barbs. It will also be noticed that the 

 barbs on the left spring obliquely and sharply from the shaft while those on the 

 right curve downwards to the juncture. 



Plate IV., Fig. 2, is the Head of a Filoplume from the Grouse, enlarged 25 

 times. Most of these filoplumes were found to have little in the way of feathery 

 structure, but it will be seen in this case that there is a distinct plumulaceous 

 character. The greater part of the filoplume consists of a long and slender 

 filament. Had it been possible to include the whole of the filoplume, it would 

 have been quite three times as long as the portion in the photograph. 



Plate IV., Fig. 3. The distal barbules of one barb spread themselves 

 over the proximal barbules of the nearest barb and effect adherence by means of 

 hooks (hamuli). In most cases the barbules are so close to each other and the 

 overlapping so dense that a representative photograph could hardly be taken ; it 

 was therefore decided to make use of a Canary Contour feather with widely 

 separated barbules. This photograph was taken with magnification of 1 30 times. 

 The hamuli are not well developed, but they may be seen here and there. Both 

 types of barbules point towards the edge of the vane, so that the hamuli on one 

 of the distal barbules hook on to several of the proximal barbules. 



Plate IV., Fig. 4, is a portion of the underside of a Barb from a Heron 

 Primary, photographed through the microscope by reflected light with a magnifi- 

 cation of 120 times. It will be seen that the brightly illuminated hamuli hang 

 in a belt about halfway along the length of the barbules. 



