. Animal physiology. Physiology, Comparative. STRUCTURE OP TUNICATA. 121 of tlie nutritive apparatus) than the corresponding parts in Articulated animals, in which the apparatus for locomotion so much predominates. 114. The group"'of Acephalous Mollusks wliicli are desti- tute of the powerJof forming a shell, includes two classes, of Avhich one does not depart widely from the general Molluscan iype, whilst the other presents 'so strong a general resem- blance to Zoophytes, that until recently it has been universally ranked with it. The first of these classes receives its name TuNiCATA fro
. Animal physiology. Physiology, Comparative. STRUCTURE OP TUNICATA. 121 of tlie nutritive apparatus) than the corresponding parts in Articulated animals, in which the apparatus for locomotion so much predominates. 114. The group"'of Acephalous Mollusks wliicli are desti- tute of the powerJof forming a shell, includes two classes, of Avhich one does not depart widely from the general Molluscan iype, whilst the other presents 'so strong a general resem- blance to Zoophytes, that until recently it has been universally ranked with it. The first of these classes receives its name TuNiCATA from the circumstance that the mantle, instead of secreting a shell, is very commonly condensed into a tough leathery or cartilaginous tunic. Many of these animals live separately, and have the power of freely moving through the water. Others are associated in comj^ound masses, of which, however, the individuals are not connected by any internal union. But others form really composite structures, like those of Zoophytes (§ 124); each individual being able to live by itself alone, but being connected by a stem and vessels with the rest. The general structure of the individuals is the same, however, in the single and in the composite animals of this class, and may be understood from the accom- b a. Fig. 63.—Social Ascidiax panying lig-ure (fig. 63). The cavity of the mantle possesses, as in the former instance, two orifices; by one of which, 6, a current of water is contmually entering, whilst by the other, a, it is as continually flowing out. These orifices lead into a large chamber, the lining of which, folded in various ways, constitutes the gills; and at the bottom of this chamber lie the stomach, e, and the intestinal canal, i, which terminates near the aperture for the exit of the Avater. All these parts. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustratio
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