Elements of zoology, or, Natural Elements of zoology, or, Natural history of animals / ed. by Reese elementsofzoolog00rees Year: 1849 504 200L0G1. this kind of aggregation, and which are ne^er found but in a solitary state. Such are the Sea-Anemones, and the Hydra, or Fresh-water Polypes. And various degrees of intimacy of con- nection between the Polypes of compound structures may be traced in different species; some of these will be hereafter noticed. 889. Whilst the real nature of polype-structures was mis- understood, their classification could not be effected on correct principles.
Elements of zoology, or, Natural Elements of zoology, or, Natural history of animals / ed. by Reese elementsofzoolog00rees Year: 1849 504 200L0G1. this kind of aggregation, and which are ne^er found but in a solitary state. Such are the Sea-Anemones, and the Hydra, or Fresh-water Polypes. And various degrees of intimacy of con- nection between the Polypes of compound structures may be traced in different species; some of these will be hereafter noticed. 889. Whilst the real nature of polype-structures was mis- understood, their classification could not be effected on correct principles. The particular form of the stem and branches of a coral cannot be assumed as a guide, for this is liable to great alteration under varying circumstances of growth, and it differs much in species, of which the structure of the individual parts is much alike. Nor can its character—as whether massive or light, stony or flexible—be correctly made the ground of pri- mary division, since some are thus associated in which the struc- ture of the living animal is very different, and others widely separated in which it is nearly allied. The only sound method is to regard the structure of the individual polypes as the basis of classification, and to draw secondary characters only from tiie circumstances of their association. In this way we shall be able to form four orders, characterized by four distinct types of structure; in each of these we shall find polypes ex- isting almost or altogether independently of one another, and species closely allied to these, in which they are intimately associated. 890. As the distinguishing characters of these orders cannot be understood without a knowledge of the structure of the polypes belonging to each, it will be better to proceed at once to the description of them—the amount of popular information on the subject being small. We shall begin with the one gene- rally accounted the simplest. Order I.—Hydroida. 891. The hydra, or fresh-water po
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