CLASS XI. 

 TUNTCATES (TUNIC AT A) 1 . 



THE Tunicates are acephalous molluscs without shells. The 

 external covering is perforated by two openings, in other respects 

 like a sac 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. SCHMIDT in Ascidia mammilaris 2 . 



The intestinal canal forms in most of the Salpce 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 FOESKAL in his 

 descriptions gave the unmeaning name of Nucleus. In Salpa pennata 

 s. cristata Cuv., 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 ossopha- 

 TIS. A furrow in the middle of the body runs from the opening 

 f the common integument, by which the water is introduced, to 

 bis commencement of the oesophagus, and serves probably to con- 

 .uct towards it the food that is conveyed with the water. [Above 

 bis furrow or semicanal, in the substance of the inner mantle is 

 n organ, called by HUXLEY endostyle, a long tubular filament 

 vith thick refracting walls. It is of various length, very short in 



1 Compare on this class : 



CUVIER Memoire sur les Thalides et les BipJiores, Ann. du Museum, IV. 1804, pp. 

 60 382, PL 68 {Memoires sur les Mollusques, No. 19) ; Memoire sur les Ascidies et 

 ur Anatomic, Mem. du Museum, n. 1815, pp. 10 39, PL i. in. (M6m. sur les 

 follusques, No. 20.) 



J. C. SAVIGNY Memoires sur les Animaux sans vertebres, II. premier fascicule, Paris, 

 8 1 6, 8vo. 



3 Zur veryleichenden Physiologic der wirbellosen Thiere, 1845, s. 6265. Extensive 

 nicroscopic investigations respecting the structure of the external covering in many 

 unicata, illustrated by beautiful figures, have been published by LOEWIG and KOELLI- 

 :ER, Ann. des Sc. natur. sieme SeVie, v. 1846, pp. 193 238. 



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