Much as the different species vary in size, from the _Ardea cocoi_ to the diminutive Variegated Heron of Azara (_Ardetta involucris_), no bigger than a Snipe, there is yet much sameness in their conformation, language, flight, nesting and other habits. They possess a snake-like head and neck, and a sharp taper beak, with which they transfix their prey as with a dart--also the serrate claw, about which so much has been said, and which has been regarded as an instance of pure adaptation. A curious circumstance has come under my observation regarding Herons. Birds in poor condition are very much infested with vermin; whether the vermin are the cause or effect of the poor condition, I do not know; but such is the fact. Now in this region (the Argentine Republic) Herons are generally very poor, a good-conditioned bird being a very rare exception; a majority of individuals are much emaciated and infested with intestinal worms; yet I have never found a bird infested with lice, though the Heron would seem a fit subject for them, and in the course of my rambles I have picked up many individuals apparently perishing from inanition. I do not wish to insinuate a belief that this immunity from vermin is due to the pectinated claw; for though the bird does scratch and clean itself with the claw, it could never rid the entire plumage from vermin by this organ, which is as ill adapted for such a purpose as for "giving a firmer hold on its slippery prey." The Spoonbill has also the serration, and is, unlike the Heron, an active vigorous bird and usually fat; yet it is much troubled with parasites, and I have found birds too weak to fly and literally swarming with them. I merely wish to call the attention of ornithologists to the fact that in the region where I have observed Herons they are exempt in a remarkable degree from external parasites.