TUN 1C AT A. 



1185 





TUNICATA. (Tunicierg, Fr.; Nackt- 

 Muscheler and See-Scheiden, Germ.) The 

 Tunlcata are molluscous animals, having no 

 calcified shell, but a more or less coriaceous 

 envelope or tunic, whence their name. This 

 external coat or test is either bag-shaped and 

 provided with two apertures, or is tube-shaped 

 and open at the ends. They have no distinct 

 head, and no organs serving as arms or feet ; 

 they are provided with a muscular and a 

 nervous system ; and with well-defined or- 

 gans of respiration, digestion, circulation, and 

 generation. 



They are exclusively marine, and are widely 

 spread from the arctic to the tropical seas. 

 Sessile or foot-stalked on the rock, or in- 

 crusting seaweed and other bodies, their 

 external form is seldom of graceful contour ; 

 yet the arrangement of the individuals in the 

 compound masses often exhibits curious and 

 elegant designs. The floating forms, however, 

 with their lengthened, sinuous chain, or 

 tapering tubes, pellucid, rainbow-tinted, or, 

 by night, brightly phosphorescent, are sur- 

 passed by no terrestrial object. The other, 

 fixed, forms, not altogether destitute of ele- 

 gance of colour in the northern seas, become 

 in warmer climates more and more rich in 

 variegated hues, and in the tropics are 

 amongst the most resplendent living gems of 

 ocean's parterres. 



The earliest notice of the tunicate animals 

 is made by Aristotle, who gives a very cor- 

 rect account of the anatomical and zoological 

 characters of a simple Ascidian, which he calls 

 TtOvov.* They, however, attracted no further 

 notice until comparatively late times. Ron- 

 deletf gives indifferent figures and descriptions. 

 Gesner and Alclrovandus, uniting Rondelet's 

 Tethya with those given by Belon J, which are 

 Alcyonia, were among the first who gave rise 

 to the confusion that long existed in the 

 history of these animals. Linnaeus in the 

 4th edition of his Systema Nature placed a 

 Tethyum in his system, under the appellation 

 of Tethys ; he pointed out at the same time 

 that the animal of bivalve Molluscs was a 

 Tethys, showing that he was aware of the 

 analogy of the Bivalves with the Tunicates. 

 In other respects, however, he added to 

 the confusion. After that Bohatsch and 

 Plancus || figured and described some species. 

 Basterlf describes a species, and gives it 

 the name of Ascidium (from aaicoc, a skin- 

 bottle), at the same time adding a very just 

 remark on the analogy of its internal struc- 

 ture with that of the oyster. This analogy 

 was noticed also by Pallas, who proposed 

 the union of the Tethyum and Ascidium **, 

 which Linnaeus carried out in the 12th edit, 

 of his Systema Naturae, uniting the species, 

 noticed by Bohatsch and Koenig, under the 



* Hist. Anim. lib. iv. c. vL, and De Part. Anim. 

 lib. vi. c. v. 



t De Piscibus, 1554. J De Aquat. 1553. 



De quibusd. Anim. Marin. 1761. 

 fl Conchis minus notis, pi. v. & vii. 1739. 

 1 Opusc. subseciv. ii. x. 5. 1764. 

 * Miscell. Zoolog. 74. 1767. 

 VOL. IV. 



name of Ascidia, and confining the name Tethys 

 to the inhabitants of the Bivalves. 



Subsequently, O.F. Muller*, O.Fabriciusf, 

 Dicquemare J, Pallas , and others, described 

 and figured several Ascidia, which Brugiere || 

 and Gmelin f collected together in their re- 

 spective works, without adding much to the 

 knowledge of the group. Cuvier's first ob- 

 servations on the simple Ascidians were begun 

 in 1797, and his memoir on their anatomy 

 was published in 1815.** About the same 

 time were published the researches of Schalkff 

 on the anatomy, and of Cams JJ on the 

 anatomy and development of the Ascidians. 

 The memoirs of Peron and Lesueur$$ on the 

 Pyrosoma, Desmarest and Lesueur || || on the 

 Botrylhis, and particularly the elaborate work 

 of Savignylli" on the simple and compound 

 Ascidians, enabled naturalists to make rapid 

 advances in the knowledge of this family. 

 With respect to the Salpians, Brown***, For- 

 skahlfff, and Tilesius JJJ were the first to 

 figure and describe any forms of this group. 

 Considerable confusion with regard to these 

 forms existed in the classifications of Linneeus, 

 Pallas, Brugiere, and Bosc, and indeed in the 

 earlier writings of Lamarck and Cuvier, 

 until the latter had an opportunity of work- 

 ing out the anatomical characters of these 

 animals. 



The earlier works on the various branches 

 of this subject have been succeeded by the 

 publication of the researches of many dis- 

 tinguished naturalists. We are chiefly in- 

 debted to the labours of Cuvier, Savigny, 

 Carus, MacLeay, and Van Beneden, for in- 

 formation on the structure and development 

 of the simple Ascidians ; to the researches of 

 Cuvier, Kuhl and Van Hasselt, Chamisso, 

 Eschricht, and Krohn, for the history of the 

 Salpians ; and to Lesueur, Desmarest, Sa- 

 vigny, Lister, Sars, Milne-Edwards, Audouin, 

 and Forbes, for our knowledge of the com- 

 pound ascidian forms. 



And, indeed, since the commencement of the 

 present century, the organisation of this group 

 has been studied with great care, rewarding the 

 labours of naturalists with discoveries of the 

 highest interest. " It was in the animal of the 

 Salpa," says Van Beneden, "that Van Hasselt 

 discovered a heart of such extraordinary 

 character, changing incessantly its auricle to 

 ventricle and its ventricle to auricle, its ar- 



* Zool. Dan. Prodromus, 1766, 



f Fauna Greenland, 1780. 



I Journal de Physique, 1777. 



| Spicilegia Zoologies, 1774, and Mem. de Pe'- 

 tersbourg. 



|| Encyclopedic Me'thodique ; Vers Mollusques, 



f Systema Naturae, edit. 13. 



** Memoires du Museum, torn. ii. 



ft De Ascidiarum Structura, Halle, 1814. 



It Meckel's Archiv, torn. ii. and Acta Cur. Nat. 

 Bonn, vol. x. 



Annales du Museum, torn. iv. 



|||| Bull. Nouv. Soc. Philom. 1815, and Journal da 

 Physique, torn. Ixxx. 



jf^f Mem. Anim. sans Vertebres, 2 e part. 

 * Natural History of Jamaica. 



tft Descript. Animalium, &c. 1776. 



ttl Ann. Hist. Nat. Leipzig, 1802. 



4 G 



