The general belief is that the pale-plumaged birds, with feathered heads and black eyes (the Roseate Spoonbill having crimson eyes), and without the bright wing-spots, the tuft on the breast, horny excrescences on the beak, and other marks, are only immature birds. Now, for one bird with all these characteristic marks of the true _Platalea ajaja_, which has a yellow tail, we meet on the pampas with not less than two to three hundred examples of the pale-plumaged bird without any traces of such marks and with a rose-coloured tail; and the disparity in number between mature and immature birds of one species could not well be so great as that. I have shot one immature specimen of the true Ajaja--so immature that it seemed not long out of the nest; but the head was bare of feathers, and it had the knobs on the upper mandible, only they were so soft that they could be indented with the nail of the finger. Azara also mentions an immature bird which he obtained, but he does not say that the head was feathered; and even this negative evidence goes a great way, since it would have been very unlike him to see a Spoonbill with a feathered head and otherwise unlike _Ajaja rosea_, and not describe it as a distinct species. There are also anatomical differences between the two birds; the pale-plumaged species having an ordinary trachea, while _A. rosea_ has a very curiously-formed trachea, unlike that of any other bird, which has been described by Garrod as follows:-- "The trachea is simple, straight, of uniform calibre, and peculiarly short, extending only two thirds down the length of the neck, where the uncomplicated syrinx is situated and the bifurcation of the bronchi occurs. The usual pair of muscles, one on each side, runs to this syrinx from above, and ceases there. The bronchi are fusiformly dilated at their commencement, where the rings which encircle them are not complete, a membrane taking their place in that portion of each tube which is contiguous to its opposite neighbour. Each bronchus, lower down, is composed of complete cartilaginous rings." [Illustration: Trachea of _Ajaja rosea_.--_a._ Trachea. _b._ Syrinx. _d._ Œsophagus. _e._ Cervical muscles. _r.b._ Right bronchus. _l.b._ Left bronchus. (From P. Z. S. 1875, p. 300.)] The woodcut of this curious structure is here reproduced by the kind permission of the Zoological Society. It is much to be wished that some one living in the Argentine Republic would devote himself to the further investigation of the history of this interesting bird, and settle the question whether there is more than one species of Argentine Spoonbill. To conclude, I may mention that the pet bird my friend kept was of the pale-plumaged species, and never lost the feathers from its head, nor did it acquire any of the characteristic marks of _P. ajaja_. Fam. XXXVIII. PHŒNICOPTERIDÆ, or FLAMINGOES.