. L'histoire naturelle. Pour l'utilisation d'écoles et les familles. Zoologie. 328 NATUEAi HISTOET.. Fig. 260.-Glaucus atlanticus. 563. Il y a un troisième ordre de l'Gasteropoda, dans lequel les branchies ne sont pas couverts dans une cavité ou chambre, qu'ils le sont dans la deuxième ordonnance, iDut soit ils ressortent à l'arrière, ou sont plus ou moins dissimulés sur les côtés dans les plis du manteau. Certains d'entre eux ont des coquillages, mais la plupart n'ont pas. Je vous donne un seul exemple, mais le glaucus, fig. 260, trouvés dans la Méditerranée et mer Indienne. Les couleurs de ces magnifiques animaux sont bleu azure et sil- ver. Les branchies forment deux ou thr

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. Natural history. For the use of schools and families. Zoology. 328 NATUEAi HISTOET.. Fig. 260.—Glaucus Atlanticus. 563. There is a third order of the Gasteropoda, in which the gills are not in a covered cavity or chamber, as they are in the second order, iDut they either stand out on the back, or are more or less concealed at the sides in folds of the mantle. Some of them have shells, but most have not. I will give but a single example, the Glaucus, Fig. 260, found in the Mediterranean and Indian Seas. The hues of these beautiful animals are azure blue and sil- ver. The gills form two or three large tufts on each side, which, besides being the breathing apparatus of the an- imal, are also its instruments frr>3dHUning. j^(^c-^ / 564. We now come to the second gi-and division of the Mollusks—the Acephalous or Headless Mollusks. These may be divided into two groups: 1. Those which have shells, called the Conchiferous, or shell-bearing. 2. Those which are covered with a leathery or membranous tunic, called the Tunicated. 565. The shells of almost all the Conchifera are bivalve. This group includes the Oysters, Clams, Mussels, Scal- lops, etc. The shell is exuded or secreted from the man- tle, and is in different layers, as may be seen in the shell of the Oyster. The outermost layer is the smallest, and as the animal grows, each layer is a little larger than the one outside of it. The two parts or valves of the shell are joined together by a hinge. Near this hinge is an elastic ligament, which allows the valves to be a little apart, which is their natural position, admitting the wa- ter freely to the mouth of the gills. When the animal wishes to shut the valves closely, it does so by means of a muscle. Sometimes there are two muscles for this purpose. 666. That you may understand the plan of the organs. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these

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• bookcentury1800
• bookdecade1880
• booksubjectzoology
• bookyear1883