398, ZOOLOGY. 
of several species of Molgula, but it has the five long decid- 
uous appendages observed in ‘young Moiguie. Among the 
compound Ascidians, Botrylius and Botrylloides have tailed 
young, while in other forms there is no metamorphosis, de- 
velopment being direct. 
Order 2. Thaliacea.—On 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 off the shores 
of Southern New England, while 
the ethers 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, 7.¢., the solitary, and 
aggregated or chain-Salpe. 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- 
Fig. 3868.—Salpa spinosa, An parent, though very thick, while 
individual from amaturechain; the outer tunic lines the cavity of 
three-quarter view, enlarged. a, 
atrial opening ; 6, mouth ; ¢, pro- “I o Cee 
fevses by which the members of tie test as in other Tunicates. In 
the chain are united ; 4, heart;”, the members of this order the oral 
nervous ganglion ; 0, nucleus; 7, ‘ 
La tes A. Agaas'z, from Ver- 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 heemal 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 nervous 
