70 Descriptions of Preparations. 



p. 77, as also in his article on ' Mollusca^ in the English Cyclo- 

 paedia. See also Professor Allman^ Fresh-water Polyzoa, 1856, 

 p. 44j seqq., and Mr. J. D. Macdonald, Transactions of the Royal 

 Society of Edinburgh^ vol. xxiii. 1862^ 1863^ for general remarks 

 on the morphology of the Tunicata. 



Much information as to the anatomy of the various orders of this 

 class will be found in the memoirs of Cuvier and Hancock, 

 already quoted; in the second volume of Savigny^s Memoires 

 sur les Animaux sans Vertebres ; in Milne-Edwards' ' Obser- 

 vations sur les Ascidies Composees/ published in the Memoires 

 de FInstitut for 1839, and in Professor Huxley's Papers in the 

 Royal Society's Transactions for 1851. 



For figures of Pyrosoma giganteum, a free social Ascidian, which 

 lend much probability to the view which has been here 

 adopted, as to the homological identity of the branchial sac 

 of the Ascidian with the gills of the Lamellibranchiata, see 

 Le Sueur, in the Bulletin des Sciences par la Societe Philo- 

 mathique, 18 15, pi. i. fig. 2, or Journal de Physique, June 

 1 8 15; and Keferstein und Ehlers, Zoologische Beitrage, 1861, 

 Taf. xii., figs. iv. and v. 



For the essential character and structure of the branchial sac, see 

 Milne-Edwards, 1. c. pp. 271-274; Hancock, I.e. pp. 327-334. 



For a description of the three tunics of the Ascidians, see Milne- 

 Edwards, 1. c. p. 270. 



For an account of the circulation in this class, see Bronn, Klassen 

 und Ordnungen des Thierreichs, iii. i. pp. 172-176; Milne- 

 Edwards, 1. c. pp. 224-228; Hancock, 1. c. pp. 321-325. 



Cuvier's and Savigny's figures of the various systems and organs of 

 Ascidians, as well as those given in V. Carus' Icones Zooto- 

 micae, tab. xviii., fi'om the most recent authorities, are well 

 worthy of being studied. 



For an account of a new genus of Ascidian which possesses a 

 bivalve shell, see Lacaze Duthiers, Ann. Sci. Nat., Ser. v. 

 torn, iv., 1865, p. 293. Sur un genre nouveau d'Ascidien, 

 Le Chrevretdius Callensis, Lac. Duth., where, at p. 307, the 

 differences between the type of organization which the animal 

 named presents and that of the Lamellibranchiata are pointed 

 out. 



