102 DR W. A. HEKDMAN ON 



which the genus stands to Salpa and Pyrosoma are pointed out. Huxley's 

 specimens had been obtained in the South Pacific between Australia and New 

 Zealand. During the next few years Krohn,* Gegenbaur^ and Leuckart^: 

 worked at the Pelagic Tunicata, but their efforts, and especially those of the 

 two former investigators, were mainly directed towards the elucidation of the 

 remarkably complex life-history of Doliolum, and the additions made to the 

 knowledge of the adult structure were comparatively few and unimportant. 



Keferstein and Ehlers, § during the winter of 1859-60, investigated several 

 Mediterranean forms of Doliolum, both as regards their anatomy and life- 

 history. As the chief subject of their observations was Doliolum denticulatum , 

 it has been of great advantage to have their description and careful figures 

 with which to compare the "Triton" specimens. No works of importance 

 upon Doliolum have appeared since, with the exception of Ulianin's || and 

 Grobben's^ papers, published during the last two years. These are mainly 

 devoted to the development and life-history, which is now almost completely 

 cleared up. Grobben, however, treats also of the anatomy and histology, and 

 to his memoir, as well as to that of Keferstein and Ehlers, I shall have to 

 refer in the following description. 



Commencing with the body form, most of the "Triton" specimens are of 

 the characteristic barrel shape (see PI. XVIII. figs. 1, 2, 3, 4, and 9), some of 

 them (as fig. 9, which was drawn from a specimen obtained August 4-5 from 

 12 fathoms) being rather wider than others. Some specimens, however (see fig. 

 10, which represents two specimens obtained on August 5th from a depth of 530 

 fathoms), are very different in shape, being narrow, elongated, and almost 

 cylindrical. At first I separated out a number of these forms, under the 

 impression that they were a distinct species from the barrel-shaped individuals, 

 but found afterwards, when examining their structure, that the two kinds 

 agreed perfectly in all the details of their anatomy. Since then I have found 

 various intermediate shapes between those shown in figs. 9 and 10, and have 

 consequently no hesitation in considering them all as one species. As a rule, I 

 find it is the specimens from considerable depths, and those which have been 

 closely packed in a tube or bottle, which diverge most from the typical barrel 



* " TJeber die Gattung Doliolum," &c, Archiv fur Naturgeschichte, 1852, p. 53. 



t " Ueber die Entwieklung von Doliolum," Zeitsehrift fur wissensch., Zoologie, 1853, Bd. v. p. 13; 

 and "Ueber die Entwicklungscyclus von Doliolum," &c, Zeitschrift fur wissensch., Zoologie, 1855, 

 Bd. vii. p. 283. 



% Zoologische Untersuchungen, Heft ii., " Salpen und Vcrwandte," Giessen, 1854. 



§ Zoologische Beitrdge,m., "Ueber dieAnatomie und Entwickclung von Doliolum," Leipzig, 1861. 



|| " TJeber die embryonale Entwieklung des Doliolum," Zoologischer Anzeiger, iv. No. 92, p. 

 472, and No. 96, p. 575, 1881; also " Zur Naturgeschichte des Doliolum," Zoologischer Anzeiger, v. 

 p. 429 and p. 447, 1882. 



IT "Doliolum und sein Generationswechsel," &c, Arheiten aus dem Zoolog. Instit. der Univ. 

 Wien, &c, t. iv. h. 2, 1882. 



