. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. ACALEPH^. 37 Body oval or circular, gelatinous, supported by an internal, solid, subcartilaginous body, and provided with very extensile tentacule-like cirri pendent from the whole of the lower sur- face. Gen. Velella. Porpita. Rataria.* Of the genera above enumerated, Eschscholtz has described about two hundred species. Messrs. Quoy and Gaimard have made us ac quainted with several others ; but of all these a comparatively small number only have been described in detail: so that, although in the account which we are now
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. ACALEPH^. 37 Body oval or circular, gelatinous, supported by an internal, solid, subcartilaginous body, and provided with very extensile tentacule-like cirri pendent from the whole of the lower sur- face. Gen. Velella. Porpita. Rataria.* Of the genera above enumerated, Eschscholtz has described about two hundred species. Messrs. Quoy and Gaimard have made us ac quainted with several others ; but of all these a comparatively small number only have been described in detail: so that, although in the account which we are now to give of the anatomy and physiology of the acalephae, we shall, for the sake of brevity, make use of the sectional designations, it must be understood that the descriptions apply only to a few species, and that, with regard to the others grouped along with these, we can only say it is probable that they are similarly con- structed. I. Locomotion. The principal organ of locomotion in the physograda is the air-filled vesicle or bladder, which exists, of various sizes, in all the species. In physalus, (Fig. 6.) it is a large organ, forming a great portion of the general mass of the animal. It is placed * The following neat but artificial arrangement of acalephae forms the subject of a communication lately made to the Zoological Society by M. Lesson, foreign member of that body : we are indebted for it to our friend Mr. Owen. I. Without a central solid axis. A. Body simple, entire. 1. Symmetrical, termi- nated at each pole by an opening .... 1 Beroidcc. 2. Non-symmetrical, the upper pole disciform or umbrlliform, imper- forate ...... 2 Medusa;. B. Body multiple or aggre- gated. a. Homogeneous. 3. Composed of two pieces adhering together, and capable of separation . 3 Diphydes. 4. Composed of numerous pieces aggregated toge- ther ...... 4 Polytomu. b. Heterogeneous. 5. Animal furnished with appendages of different kinds. * Vesicle small, regular, placed at the summit of a kind o
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