on the Nestling of Fraser's Totiracou. 59


Fig. 2. A highly magnified portion of one of the barbules from

a barb of a nestling down feather of the Hoatzin.

Compare this with the round bamboo-like structure

of the Touracou {text fig. 1).


Fig. 2 a. A nestling down feather of the Hoatzin, magnified, also

borne on the tip of a developing contour feather,

though only the tip of the latter is shown.


III. Structure of the Nestling-down.


The nestling down is represented only by what I have else¬

where called pre-penna, that is to say by down feathers which

are immediately succeeded by contour feathers. Pre-plumulae,

or down feathers succeeded later by down feathers, are wanting.


The pre-pennse are of the umbelliform type (text fig. 1 a),

that is to say they have no distinct shaft, but are composed of a

number of rami or barbs arising from a common base. These

rami are relatively short and bear numerous short radii or bar¬

bules, which cease some distance from the end of the ramus

(text fig. 1 a).


Under the microscope each radius is seen to be made up

of a series of rounded rods fitting apparent^ one into another

like the sections of a fishing rod (text fig. 1).


In text fig. 1 a the pre-penna is seen in the process of being

borne out by the definitive, or adult feathers (df.). Concerning

the latter I would remark that there are some points which

demand further investigation. It may prove that this apparently

definitive feather is really what is known as a mesoptile or

intermediate stage between the nestling down and the adult

feather.


Here we may mention that the pre-penna of Fraser’s

Touracou differs conspicuously from the similar feathers of the

Hoatzin (text fig. 2). In this bird it will be noticed the barbules

or radii are shorter, and more thickly clustered. Microscopically

examined it will be found that, while in the Touracou the radii

are in the form of jointed rods , in the Hoatzin they take the

form of flattened, ribbon like plates produced, at each joint, into

short processes or fila (text fig . 2 f). Moreover the segments are

longer in the Touracou than in the Hoatzin.



