II STRUCTURE OF ASCIDIA 39 
2) 
of Todaro, Brooks,! Salensky,? Seeliger,> Korotneff and others 
have elucidated the embryology, the gemmation and the life- 
history of the Salpidae; and Grobben, Barrois,? and more 
especially Uljanin,® have elaborately worked out the structure 
and the details of the complicated life-history of the Doliolidae. 
Finally we owe to the labours of Metschnikoff, Kowalevsky, 
Giard, Hjort, Seeliger, Ritter, Van Beneden and Julin, much 
detailed information as to development and life-history, the 
process of gemmation and the formation of colonies, which has 
added greatly to our knowledge of the position and affinities of 
the Tunicata and of their natural classification. 
Structure of a Typical Ascidian. 
If a typical “Simple Ascidian,” such as the common British 
Ascidia mentula (Fig. 15), or Ascidia virginea, be examined alive 
and expanded in sea-water it will be seen to bear on the upper 
surface two short projections, each terminated by a wide tubular 
opening, through which the aninal, when touched, can emit jets 
of water with considerable force —thus accounting for the 
popular name “sea-squirts.” The rest of the body is covered by 
the dull grey tough cuticular outer “test” or “tunic” (hence 
Tunicata) by means of which the animal is attached to a rock 
or other foreign body. One of the tubular openings, the mouth or 
“branchial aperture,” is terminal, and indicates the morphological 
anterior end; it is surrounded by eight lobes. The other opening, 
the cloaca or “atrial aperture,” is on the dorsal edge, from one- 
third to one-half way down the body, and is bounded by six lobes 
only ; consequently the two apertures, and so the ends of the 
body, can be distinguished externally by the number of lobes— 
an important matter. The area of attachment is usually the 
posterior part of the left side; in Fig. 15 the animal is seen 
from the right hand side. 
If a little carmine-powder, or some other insoluble particles 
be scattered in the water in which the Ascidian is living, the 
“The Genus Salpa,” Mem. J. Hopkins Univ. 1893. 
Zeits. wiss. Zool. 1876, 1878 ; Mitth. Zool. Stat. Neapel, 1883, etc. 
Jen. Zeitschr. 1886, 1888, etc. ; also Bronn’s Thier-Reich. 
Mitth. Zool. Stat. Neapel, 1893 and 1897 ; and Zetts. wiss. Zool. 1895 and 1896. 
Journ. Anat. Phys. Paris, xxi. 1885. 
Fauna and Flora G. v. Neapel, Monogr. x. 1884. 
ou Pod o rw = 
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