The second wall-case contains further illustrations of the anatomy of Birds. In the left-hand part a series of wings of Birds displays the form characteristic of different groups; while above them are a few of the different types of tails, supplementing the series of tails in the table-case. Very instructive is a series of skins of white chickens of the same brood at different ages, displaying the gradual replacement of the down by the adult plumage. The table-case in the middle of the bay contains illustrations of the external characters, the beak, the feathers, and the tail, as well as of the fore and hind limbs, or wings and feet. By the aid of the explanatory labels, the essential characters and the principal modifications of all these parts may easily be followed. Two cases on the wall in the vestibule leading to the Fish Gallery illustrate the chief modifications of the eggs of Birds, and their differences in structure, number, form, size, texture of surface, and colour. On the side of the main staircase opposite are specimens illustrating the parasitic nesting habits of certain Cuckoos and various other Birds; while near by is a remarkably fine series of the eggs of Cuckoos with those of the Birds among which they were respectively deposited. On the opposite (east) side of the staircase the visitor will find a case showing the remarkable variation in colouring and markings displayed by the eggs of the Guillemot. [Sidenote: Bay IV. General structure of Reptiles and Amphibians.] The fourth bay on the west side of the hall exhibits the leading peculiarities in the structure of Reptiles and Amphibians. Owing to the large number of groups in the former class now extinct, many fossil specimens, or plaster reproductions of the same, are shown. The wall-case on the south side of this bay illustrates the different ordinal groups of Reptiles--living and extinct. Very instructive are the skeletons of Tortoises and Turtles, showing the relations of the vertebræ and limb-bones to the bony part of the shell. Lizards and Snakes are mostly represented by coloured casts. The extinct Dinosaurs are represented by a small-sized model of _Iguanodon_, together with a photograph of the skeleton and a plaster-cast of the bones of the hind-foot showing the three toes. The adjacent side of the table-case shows the modifications of the backbone, or vertebral column, of the ribs, and of the limbs, in the different groups of the class. Specially noticeable are examples of five types of Skink-like Lizards, exhibiting the gradual diminution in the size of the limbs and their final disappearance.