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CLASS XI. 
TUNICATES (TUNICATA):. 
Tue Tunicates are acephalous molluscs without shells. The 
external covering is perforated by two openings, in other respects 
like a sae and entirely closed, of various thickness and hardness, in 
some gelatinous, in others leathery. It consists of a tissue that is 
sometimes very composite, includes cells, fibres, nuclei, crystals also 
of carbonate of lime, and of which the fundamental matter contains 
no nitrogen, but only oxygen and hydrogen, and agrees in compo- 
sition with the vegetable cell-membrane (cellulose), as was first 
discovered by C. ScuMmipr in Asctdia mammilaris ’*. 
The intestinal canal forms in most of the Sal/pe some convolu- 
tions, which are united to form a clue which occupies a small part 
alone of the cavity of the body, and to which ForskAt in his 
descriptions gave the unmeaning name of Nucleus. In Salpa pennata 
s. cristata Cuy., however, the intestinal canal runs straight from 
the mouth to the opposite end, and has, close above and behind the 
mouth, an expansion or stomach that terminates blindly and lies in 
the opposite direction. The mouth, placed internally and bordered 
by a tortuous band, is properly only the beginning of the cesopha- 
gus. <A furrow in the middle of the body runs from the opening 
of the common integument, by which the water is introduced, to 
this commencement of the cesophagus, and serves probably to con- 
duct towards it the food that is conveyed with the water. [Above 
this furrow or semicanal, in the substance of the inner mantle is 
an organ, called by Hux ey endostyle, a long tubular filament 
with thick refracting walls. It is of various length, very short in 
1 Compare on this class : 
Cuvier Mémoire sur les Thalides et les Biphores, Ann. du Muséum, tv. 1804, pp. 
360—382, Pl. 68 (Mémoires sur les Mollusques, No. 19); Mémoire sur les Ascidies et 
leur Anatomie, Mém. du Muséum, 11. 1815, pp. to—39, Pl. 1.—111. (Mém. sur les 
Mollusques, No. 20.) 
J.C. Savieny Mémoires sur les Animaua sans vertebres, 1. premier fascicule, Paris, 
1816, Svo. 
2 Zur vergleichenden Physiologie der wirbellosen Thiere, 1845, 8. 62—65. Extensive 
microscopic investigations respecting the structure of the external covering in many 
tunicata, illustrated by beautiful figures, have been published by Lorwie and Kog.ut- 
KER, Ann. des Sc. natur, 3itme Série, v. 1846, pp. 193—238. 
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