File:Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct - for the use of schools and colleges (1870) (14596030009).jpg

Identifier: outlinesofcompar00agas (find matches)
Title: Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges
Year: 1870 (1870s)
Authors: Agassiz, Louis, 1807-1873 Gould, Augustus A. (Augustus Addison), 1805-1866 Wright, Thomas, 1809-1884
Subjects: Physiology, Comparative Zoology
Publisher: London : Bell & Daldy
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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Text Appearing Before Image:
Apiocrinus rotunda. Fig. 73.âEncrinus moniliformi* THE SKELETON OF MOLLUSCA. 103 tremity of which the eyes are situated, corresponding to theirposition in the echinidse ; the summits of the arese being ana-logous to the extremities of the rays bent up towards theanal pole. In the CKIKOIDEJE, or sea lilies, which may be likened tosea-stars supported upon many jointed columns, the skeleton isvery complicated, being composed of many thousand separatepieces, beautifully and nicely fitted to each other. Fig. 72represents the pear encrinite (Apiocrinus rotunda), from theBradford clay ; and fig. 73, the lily encrinite (Encrinus mo-niliformis), from the Muschelkalk. These stalked echinodermsattained a great generic development in the palaeozoic rocks,entire strata being sometimes composed of their brokenskeletons ; their forms are less numerous in the triasic andoolitic periods ; a few only are found in the chalk, and onerare species lives in the warm regions of our present seas.âT. W.)
Text Appearing After Image:
Fig. 74.âCyprceacdssis rufa; a, mature, b, immature state of the same shell. ⢠§ 220. In the mollusca, the solid parts are secreted by theskin, most frequently in the form of a calcareous shell of one,two, or many pieces, serving for the protection of the soft 104 THE SKELETON OF MOLLUSCA. parts which they cover. These shells are generally so con-structed as to aiford complete protection to the animal withintheir cavities. In a few, the shell is too small for this pur-pose ; in others it exists only at a very early period, and islost as the animal is developed., so that at last there is noother covering than a slimy skin. In some the tegumentarymembrane becomes so thick and firm as to have the consistenceof elastic leather, or it is gelatinous or transparent; and whatis very curious, these tissues may be the same as those of woodyfibre, as, for example, in the ascidia. In general the solid partsdo not aid in locomotion, so that the mollusca are mostly slug-gish in their movements

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