M. Ussow's ZooJoyico-Emhryological foresfujotwus. ;i21 



THE TUNICATA. 



Witli tlie more accurate knowledge of tlie anatomy, and 

 especially of tlie developmental history, of the various species 

 of Tunicata, the notion of the alliance of these animals with 

 the Mollusca (Acephala, Molluscoidea, Ilimatega), which was 

 for a long time predominant, iinds fewer and fewer adherents 

 among modem zoologists*. Since the appearance of the 

 epoch-making work of A. Kowalevskyf on the embryology 

 of the simple Ascidia, and of some later| no less pregnant 

 and interesting investigations of the same naturalist relating 

 to the same subject, besides the works of Kupfer§, E. Metsch- 

 nikoff II, Ganin ^, &c., which have confirmed and completed 

 the results obtained by Kowalcvsky, the notion of the phylo- 

 genetic relationship of the Tunicata to the Vertebrata, and 

 indeed to their lowest form {Amphioxiis), has gained ground 

 in science. That the separation of the Tunicata from the 

 molluscan tyj)e has become necessary in consequence of the 

 investigations just cited is now admitted more or less by 

 all zoologists — some of them, such as Gegenbaur** and 

 E. Ilackelft, regarding it as possible to refer the Tunicata 

 to the Vermes; whilst others, such as Oscar Schmidt |:}:, who 

 desire to see classification founded chiefly upon embryological 

 data, form with them a special distinct class of Primitive 

 Vertebrates. On the other hand, there are still a good many 

 naturalists (Lacaze-Duthiers§§, Donitz ihl, Hertwig^^, Von 

 Baer***) who deny all relationship with the Vertebrata to 



* Hiickel, Gen. Morph. Bd. ii. pp. cvi, cvii, 413 ; Gegeubaur, Vergl. 

 Anat. 2te Aufl. p. 474 ; Huxley, Couip. Anat., Le.ss. v. 



t " Entsvickelungsgesch. der einf. Ascid.," M^ru. de I'Acad. de St. 

 P^tersb. tomex. 1866. 



X "Weitere Studien iiber die Entw. der einf. Ascid.," Archiv fiirmikr. 

 Anat. Bd. vii. p. 101 ; Nachr. der K. Ges. der Wiss. p. 401, and for 1808 ; 

 " Ueber die Knosp. der Perophora Listein, Wiegm.," Kiew Zapiski, Bd. iii, 

 Div. 1 ; Zeitschr. fiir -wns.'. Zool. 1871, p. 28o. ' 



§ Arch, fur mikT. Anat. 1869, p. 459, 1870, p. 116, 1872, p. 368. 



II Bull, de I'Acad. de St. Pt^tersb. tome xiii. p. 293, 1869 ; Zeitschr. fiir 

 wis.s. Zool. xxii. p. ;3;39, 1872. 



il "Neue Thatsachen aus der Entwickelungsgesch. der Ascid.," Zeitschr. 

 fiir wiss. Zool. 1870, p. 512. 



** Verorl. Anat. 2te Aufl. (1870). pp. 158, 474. 



tt Natiirl. Schopfungsgesch. 4te Aufl. (1873), pp. 448, 4G6, 467. 



tt Vergl. Anat. 6te Aufl. (1872), p. 248. 



§§ " Rech. sur Torgan. et rerabrvog. des A.scidies," Comptes Rendua, 

 1870, p. 1154. 



III! Arch, fur Phv.*iol. 1870. p. 762. 



illl .Ten. Zeitschr. Rd. vii. (1872), p. 46. 



*** M^ra. de TAcad. de St. P^tersb. tome xix. ( 1873). 



