ii STRUCTURE OF ASCIDIA 39 



of Todaro, Brooks, 1 Salensky, 2 Seeliger, 8 Korotneff, 4 and others 

 have elucidated the embryology, the gemmation and the life- 

 history of the Salpidae ; and Grobben, Barrois, 5 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, Eitter, 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. lo\or Ascidia mrginea, 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 animal, 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. 1 5 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 



1 "The Genus Salpa," Mem. J. Hopkins Univ. 1893. 



- Zeits. wiss. Zool. 1876, 1878 ; Mitth. Zool. Stat. Neapel, 1883, etc. 



3 Jen. Zeitschr. 1886, 1888, etc. ; also Bronn's Thicr-Reich. 



4 Mitth. Zool. Stat. Neapel, 1893 and 1897 ; and Zeits. wiss. Zool. 1895 and 1896. 



5 Journ. Anat. Phys. Paris, xxi. 1885. 



6 Fauna and Flora G. v. Neapel, Monogr. x. 1884. 



