86 



THE HUMMING BIRD. 



[November i, 1891 



The reproduction of Mollusks is in all cases effected 

 by means of eggs. The number of eggs produced by 

 some bivalves is enormous. The common Oyster is 

 said to produce a million or more, and the American 

 variety ten, or even sixty, times as many. Terrestrial 

 Mollusks are not so prolific. They deposit but very 

 few eggs ; but in certain groups, such as the large 

 South American Bulimi, and the African Achatinae, 

 they are protected by a hardened calcareous shell, 

 and approaches in size a pigeon's egg. 



Very little is known about the limits of age of 

 Mollusks. It is very probable that they live for a 

 considerable period. They have the faculty to hiber- 

 nate in cold climates, and to assume a state of 

 torpidity in tropical countries, closing up the aperture 

 of their shells with a temporary lid or door (epiphragm), 

 in order to resist to the dryness of the atmosphere or 

 to the cold. When the warmth and rain re-appears, 

 they revive, and are seen crawling in every 

 direction. 



Mollusca made their appearance on the globe at a 

 very early date, and a large number of fossil forms 

 have been found. The great number are inhabitants 

 of the sea ; some are found in rivers and lakes, and 

 others live on land, on mountains, in valleys, forests, 

 etc. Hence their designation as Marine, Fluvatile, or 

 Land Shells. 



Case 1 contains the Chepalopods, including the 

 Octopus, Cuttlefish, Squid, Spirula, the Paper and 

 Pearly Nautilus. Case ie includes the Pteropods, 

 called also Sea Butterflies. 



Cases ie — 17D contain the Gastropods, including 

 the Conidae, or Cones, one of the most beautiful of 

 families of Shells, of which about 400 species are 

 known. They are beautiful shells, and highly prized 

 by the amateurs. ^50 has been paid for a single 

 shell. Next to the Cones come the Terebridae, or 

 Auger Shells ; the Pteuromatidae, or Slitslips ; the 

 Muricidae, or Rock Shells ; the Buccinidae ; the 

 Olividae, or Olives ; the Harpidae, or Harps ; the 

 Fasciolaridae, the Mitridae, or Mitras ; the Volutidae, or 

 Volutes ; the Cassididae, or Helmet Shells ; the 

 Doliidae, or Tun Shells ; the Cypreidae, or Cowry 

 Shells ; the Cyciophoridae and Helicinidae, etc., etc. 

 The Olives, Harps, Mitras, Volutes, and Cowry Shells 

 are highly prized by collectors in consequence of their 

 variety in colour and their beauty. 



Cases 12G to 17D includes the Pulmonata or Land 

 and Fluviatile Shells; such as Helicidae, or Land 

 Snails ; Limacidae, or Slugs ; Limnœidae, or Fresh- 

 water Snails, etc. Many species of Helix are usually 

 eaten. About 15,600 species are known. 



Cases 17E to 26B includes the Pelecypoda, or 

 Bivalves ; such as Venus-Shells, Cockles, Razor Shells, 

 Clams, Piddocks, Ship Worms, Sea and Fresh-water 

 Mussels, and the well-known Oysters, of which many 

 species are known, many of them good to eat, and 

 producing occasionally pearls ; but the finest of them 

 are found in Meleagrina margaritifera, or Pearl 

 Oyster, which is found abundantly in Ceylon and West 

 Australia. It has a very strong shell, lined with thick 

 layers of mother-of-pearl. Hundreds of tons of 

 these shells are annually imported into Europe, where 

 they sell at a very good price. 



It is employed in many industries. The nacre is 

 generally of a pearly-white colour, rarely dark, and 

 occasionally almost black. The pearl is the produce 

 of the effort of the animal to get rid of the irritation 

 caused by a foreign substance between its valves, and 

 by covering it with nacre. 



One of the most ancient, and, at the present day, 

 the most important of the pearl fisheries is that 

 carried on in Ceylon. The banks on which the 

 oysters grow are at an average depth of 30 to 60 ft., 

 and extend several miles. The oysters, which should 

 be six or seven years old when 'collected, are 

 gathered in baskets by divers and hauled up by ropes 

 into hundreds of small boats. The shells are then 

 brought to land and left to die ; then they are 

 minutely examined for the pearls, which are either 

 found loose in the shells or embedded in the fleshy 

 parts of the oysters. As many as two million of 

 oysters have been brought ashore in a single day. 

 A small proportion of the oysters contain pearls ; in 

 some they are very small (seed, or dust-pearls, 

 as they are called), and very few contain pearls 

 larger than a pea, which are so highly valued. A 

 very fine pearl can be bought at Ceylon for ^40. 

 The Chinese obtain pearls artificially from a species 

 of fresh-water Mussel, Dipsas plicata. In order to 

 do this, they keep them in tanks and insert between 

 the shell and the animal either small shot or small 

 round pieces of mother-of-pearl, which soon receive 

 regular coatings of nacre, and assume the look of 

 ordinary pearls. 



Case 26H and last contains the Brachiopoda, 

 which are now considered by some naturalists to be 

 more related to Annelids, or Marine Worms, than to 

 Mollusca. Others maintain that their affinities lie 

 rather with Polyzoa and Tunicata, with which they 

 form a distinct class termed Molluscoida. As a 

 whole, the collection of shells of the British Museum 

 is one of the most complete known, and contains a 

 large number of types and rarieties. One of the best 

 acquisitions was that of the celebrated collection of 

 the late Hugh Cuming, of London. 



GALLERY OF CETACEA. 



For want of space, the collection of Cetacea has 

 been located in a large room in the basement, which 

 has the disadvantage of not being well lighted ; but a 

 better accommodation will be afforded to them when 

 the west front of the building will be erected. The 

 exhibition of Cetacea is limited to the skeletons of 

 the larger species. 



On entering, on the left side of the door, near the 

 window is a case containing a stuffed specimen, 

 skeleton, and several skulls of the very curious Fresh- 

 water Dolphin, Platanista gangetica, and in the next 

 case the peculiar Dolphin of the river Amazon, Inia 

 geoffrensis. Among the other interesting species can 

 be seen 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 abortive 

 (as shown in the specimen by removal of part of the 



