. Zoology for high schools and colleges. Zoology. 398 ZOOLOGY. of several species of Molgula, but it has the five long decid- uous appendages observed in young MolgulcB. Among the compound Ascidians, Botryllus and Botrylloides have tailed young, while in other forms there is no metamorphosis, de- velopment being direct. Order 3. Thaliacea.—Oil the whole, we may regard this order, represented by Salpa (Fig. 386°), and Doliolum, as comprising the more specialized forms of Tunicates. Salpa is pelagic, one species occurring in abundance ofE the shores of Southern New England, while the others most
. Zoology for high schools and colleges. Zoology. 398 ZOOLOGY. of several species of Molgula, but it has the five long decid- uous appendages observed in young MolgulcB. Among the compound Ascidians, Botryllus and Botrylloides have tailed young, while in other forms there is no metamorphosis, de- velopment being direct. Order 3. Thaliacea.—Oil the whole, we may regard this order, represented by Salpa (Fig. 386°), and Doliolum, as comprising the more specialized forms of Tunicates. Salpa is pelagic, one species occurring in abundance ofE the shores of Southern New England, while the others mostly live on the high seas all over the tropical and sub- tropical regions of the globe. Late in the summer our Salpa spinosa of Otto can be captured in multi- tudes by the tow-net in Long Island Sound. There are in Salpa two kinds of individuals, :, the solitary, and aggregated or chain-Salpse. The body of the solitary or asexual form is more or less barrel-shaped, with a series of circular bands of muscles, like the hoops of a barrel, and situated on the inner side of the outer tunic. The test is trans- parent, though very thick, while the outer tunic lines the cavity of the test as in other Tunicates. In the members of this order the oral aperture of the mantle is at one end of the body, and the atrial opening at the opposite end, the minute digestive canal be- ing but slightly curved, the body-cavity being largely occu- pied by the pharyngeal or respiratory sac. Moreover, the dor- sal or hasmal side of the body is clearly distinguishable from the ventral or neural side, as well seen in Doliolum, where the well-marked tubular heart lies above the digestive organs, and is directly opposed, as in worms generally, to the nervoua. Wg. 386'.—SaZpa spinosa. An individual from a mature chain; ttiree-quarter view, enlarged, a, atrial opening ; b, moutli; c, pro- ce-^Bes l)y which the members of the chain are united ; A, heart; n, nervous ganglion ; o, nucleus ; r, gill.—Afte
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