Abstract
The correspondence of events in the germ and definitive feather pattern characteristics is implicit in the relations which Lillie and Juhn have shown to exist in the collar during the reaction of barbs at all levels to high concentrations of thyroxin and female hormone. From this point of view measurable elements of pattern are of direct developmental and physiological significance. Definitive pattern relations are also of direct importance in other respects, as in the quantitative formulation of symmetry relations. We report here methods which have been developed to give the desired data.
The characteristics of the definitive feather which can be measured are distances between barbs on rhachis, lengths of barbs, and lengths of pattern elements within the limits of definition as barb or rhachis segment. Barbule lengths and distances between barbules may also be measured in certain instances.
(a) Mounting the feather. In order to obtain the desired measurements on barb length and barb frequency with precision and reasonable rapidity it is necessary that the feather be permanently mounted with reference to simplest possible axes, i. e., with barbs at right angles to rhachis.
The rhachis of the feather is first set in paraffine, applied hot, on the glazed surface of heavy bristol board. The barbs are then brushed out until they lie approximately at right angles to the rhachis. The bristol board is now clamped down on a base movable in the line of and exactly parallel to the rhachis. Above this sliding frame and at right angles to its line of motion is a guide bar.
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