In the same gallery are exhibited examples of three other groups of marine organisms, respectively known as Polyzoa, Brachiopoda, and Tunicata. The Polyzoa live in colonies, and include the so-called Sea-Mat. They are often mistaken for sea-weeds, although in reality they are animals of comparatively high organisation. The Brachiopods have two shells like Bivalve Molluscs, but the valves are dorsal and ventral—that is to say, back and front—instead of right and left. One valve is frequently perforated, hence the name of “Lamp-shells,” from a resemblance to an ancient Roman lamp. Sea-squirts, Tunicates, or Ascidians, are worthy of the attention of the visitor on account of their affinity with the Vertebrate stock, of which they may be regarded as a degenerate type. It is in the larvæ or “Ascidian Tadpoles” that the evidence of Vertebrate relationship is most conspicuous, as shown by certain important characters in the nervous system, skeleton, and respiratory organs.
A series of large shells occupies some of the space in the wall-cases, among which attention may be directed to the thick and often handsomely coloured Helmet-shells (Cassis), which, together with the pink Queen-conch (Strombus), were formerly largely used in the now nearly obsolete art of cameo-cutting. In addition to these, a selection of British shells, and series of the eggs of Molluscs, as well as specimens illustrating the formation of pearls, and other points of special interest connected with Molluscs, are displayed. These specimens include not only the Pearl-oyster, but some of the other shells used in the mother-of-pearl trade.
Whale-Room.
Whale-Room.
Approached by a staircase, leading down from the last (or western-most) of the passages which connect the Bird-gallery with the Coral-gallery, is a separate room in which are placed the specimens of Whales and their relatives. For these, on account of their large size, no other place could be found in the Museum; but the room has, unfortunately, the disadvantage of being too small to display such large animals to full advantage. It is also intersected by columns, which interfere with the complete view of the larger specimens.
As it is almost impracticable to preserve the skins of the larger species of Whales, owing to the oil with which they are saturated, the exhibition of the characters of these animals is carried out by means of their skeletons and artificial models of one side of the body. Complete models, which are much better than actual skins, of many of the smaller kinds, are shown. A general account of the structure and classification of the Cetacea, as Whales are technically termed, with reference to those exhibited in this gallery, will be found in a Special Guide.[16]
Fresh-water Dolphins.
Narwhal.
On the left side of the entrance is a case containing a stuffed specimen, a skeleton, and several skulls of the Susu, or Fresh-water Dolphin (Platanista gangetica) of the rivers of India, and also of the Dolphins of the Rio de la Plata (Pontoporia blainvillei) and of the River Amazon (Inia geoffroyensis). Among the specimens fronting the visitor as he enters the room, one of the most interesting, on account of its remarkable dentition, is the Narwhal, or Sea-Unicorn. It has only two teeth, which lie horizontally in the upper jaw. In the female both remain permanently concealed within the bone of the jaw, so that this sex is practically toothless; but in the male, while the right tooth remains similarly concealed and rudimentary (as shown in the specimen, by removal of part of the bone which covered it), the left is immensely developed, attaining a length equal to that of half the entire animal, and projecting horizontally from the head in the form of a long, straight, tapering and pointed tusk, spirally grooved on the surface. In rare cases, as in the skull exhibited near the skeleton, both teeth are fully developed, and it is noticeable that in such specimens the direction of the spiral is the same in both tusks.
Sperm-Whale.