M. Ussow’s Zoologico-Embryological Investigations. 321 
TE LUNICATA. 
With the more accurate knowledge of the anatomy, and 
especially of the developmental history, of the various species 
of Tunicata, the notion of the alliance of these animals with 
the Mollusca (Acephala, Molluscoidea, Himatega), which was 
for a long time predominant, finds fewer and fewer adherents 
among modern zoologists*. Since the appearance of the 
epoch-making work of A. Kowalevsky{ 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||, Ganin §], &c., which have confirmed and completed 
the results obtained by Kowalevsky, the notion of the phylo- 
genetic relationship of the Tunicata to the Vertebrata, and 
indeed to their lowest form (Amphioxus), has gained ground 
in science. ‘That the separation of the Tunicata from the 
molluscan type 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 
i. Hiickel], regarding it as possible to refer the Tunicata 
to the Vermes; whilst others, such as Oscar Schmidt{t, 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 |||, Hertwig {/{], Von 
Baer***) who deny ail relationship with the Vertebrata to 
* Hackel, Gen. Morph. Bd. ii. pp. evi, evii, 413; Gegenbaur, Vere. 
Anat. 2te Aufl. p. 474; Huxley, Comp. Anat., Less. v. 
+ “ Entwickelungsgesch. der einf. Ascid.,’” Mém. de l’Acad. de St. 
Pétersb. tome x. 1866. 
{ “ Weitere Studien tiber die Entw. der einf. Ascid.,” Archiv fiir mikr. 
Anat. Bd. vii. p. 101; Nachr. der K. Ges. der Wiss. p. 401, and for 1868 ; 
“Ueber die Knosp. der Perophora Listeri, Wiegm.,”’ Kiew Zapiski, Bd. iii, 
Div. 1; Zeitschr. fiir wiss. Zool, 1871, p. 285. 
§ Arch. fiir mikr, Anat. 1869, p. 459, 1870, p. 115, 1872, p. 358. 
|| Bull. de Acad. de St. Pétersh. tome xiii. p. 293, 1869; Zeitschr. fiir 
wiss. Zool. xxii. p. 339, 1872. : 
4] ‘Neue Thatsachen aus der Entwickelungsgesch. der Ascid.,” Zeitschr. 
fiir wiss. Zool. 1870, p. 512. 
** Vergl. Anat. 2te Aufl. (1870), pp. 158, 474. 
tt Naturl. Schépfungsgesch. 4te Aufl. (1873), pp. 448, 466, 467. 
t{ Vergl. Anat. 6te Aufl. (1872), p. 248. 
§§ “Rech. sur l’organ. et ’embryog. des Ascidies,” Comptes Rendus, 
1870, p. 1154. 
||| Arch. fiir Physiol. 1870, p. 762. 
qq Jen. Zeitschr. Bd. vii. ($872), p. 46. 
*## Mém. de l’Acad. de St. Pétersb. tome xix. (1873). 
