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The animal kingdom, arranged after its organization : forming a natural history of animals, and an introduction to comparative anatomy . beproperly said to commence, unless we give to the term generation a much wider acceptation than it hashitherto possessed. We shall have to return to this subject, when considering the curious relations which subsistbetween certain Polypes and Medusm, in the Appendix to the Radiata. 11. In the Ascidiad;e, the body is either fixed immediately to some solid mass, or is attached by a peduncle ;the two orifices of the mantle are usually near each other (Fig. 8) ;

The animal kingdom, arranged after its organization : forming a natural history of animals, and an introduction to comparative anatomy . beproperly said to commence, unless we give to the term generation a much wider acceptation than it hashitherto possessed. We shall have to return to this subject, when considering the curious relations which subsistbetween certain Polypes and Medusm, in the Appendix to the Radiata. 11. In the Ascidiad;e, the body is either fixed immediately to some solid mass, or is attached by a peduncle ;the two orifices of the mantle are usually near each other (Fig. 8) ; Stock Photo
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The Reading Room / Alamy Stock Photo

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2AJ88YB

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7.1 MB (361.8 KB Compressed download)

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1864 x 1340 px | 31.6 x 22.7 cm | 12.4 x 8.9 inches | 150dpi

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The animal kingdom, arranged after its organization : forming a natural history of animals, and an introduction to comparative anatomy . beproperly said to commence, unless we give to the term generation a much wider acceptation than it hashitherto possessed. We shall have to return to this subject, when considering the curious relations which subsistbetween certain Polypes and Medusm, in the Appendix to the Radiata. 11. In the Ascidiad;e, the body is either fixed immediately to some solid mass, or is attached by a peduncle ;the two orifices of the mantle are usually near each other (Fig. 8) ; the greater part of the internal cavity isoccupied by the branchial sac, which may be regarded as a dilated pharynx ; and the viscera occupy a compara-tively small space at the bottom of this sac. (See Fig. 7.) This order may be divided into the three families ofsimple, social, and compomid Ascidians. 1. The Simple Ascidians are completely detached from another ; for, although frequently met with in groups orclusters, the individuals composing these have no organic union. They generally approach the oval form. They MOLLUSCA. 671. Fig. 7.-orifice, orcanal; t, co have only one method of multipUcation ; namely-oy means of eggs. To this division belong the genera AsddiaOynthia, PhaUusia, Boltenia, with some others. 2. The Social Ascidians adhere to soUd bodies by a sort of root or creeping stem, which runs along their surface, and which puts forth reproduetive buds that develope new individuals ; whence it results that these animals live in^ clusters or colonies, of which the several individuals are organi- cally united. Each animal has its own heart, respiratory ap-paratus, and system of nutrition ; but a common circulationof blood extends through the stem and branches, connectingthem all with each other. The relation between the separateanimals thus bears a strong resemblance to that which sub-sists among the individual polypes of a SertvXaria or othercompound polypidom, in whose

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