38 THE VOYAGE OF H.M.S. CHALLENGER. 



Branchial Sac usually of moderate size, occupying the anterior lialf or three- 

 quarters of the body. Its wall contains transverse and fine longitudinal 

 vessels, separated by stigmata, but no internal longitudinal bars, and it is 

 never folded. The stigmata are placed transversely, and vary in number 

 from five to fifty or more on each side of the sac. 



Dorsal Lamina and Tentacles absent. 



Nerve Ganglion placed in the median dorsal line, a little anterior to the middle 

 of the bod}', and Ijetween the third and fourth muscle bands. 



Dorsal Tubercle placed some distance in front of the nerve ganglion, and sur- 

 rounded by the spii-ally- coiled dorsal ends of the peripharyngeal bands. 



Alimentary Canal placed ventrally, behind the branchial sac. 



Reproductive Organs ventral, opening into peribranchial cavity near to anus. 

 A tailed larva is formed. 



This genus was formed in 1835 by Quoy and Gaimard' for the reception of two 

 species of pelagic Tunicates which were found near the islands Amboina and Vanikoro, 

 in the Bauda Sea, during the voyage of the " Astrolabe " round the world, under 

 Dumont d'Urville. The name Doliolum had, however, been applied twelve years before 

 by Otto " to the gelatinous " Haus " of the crustacean Phronima sedentaria. But as 

 that object is merely a part of the test of a dead Tunicate, the specific names employed 

 by Otto and Delle Chiaje, and the generic name Doliolum as applied to the Phronima 

 covering, must lajDse, and therefore there need be no difficulty in retaining that name 

 in the sense in which it was used by Quoy and Gaimard. 



Quoy and Gaimard described and figured little more than the external appearance 

 of their two forms of Doliolum. They placed the genus correctly enough near Salpa 

 amongst the pelagic Tunicata, and they characterised it by its barrel-like form, its 

 terminal apertures, its encircling muscle bands (which, however, they mistook for 

 vessels), and its internal branchia (the anatomy of which they seem to have quite 

 misunderstood)'. The two species they describe are Doliolum denticidatum and 

 Doliolum caudatum, the latter being undoubtedly a "nurse" form or blastozooid. 

 They add nothing further in regard to the internal structure of the animals, and the 

 short descriptions and the figures are scarcely sufficient to determine the species, beyond 

 showing that their Doliolum denticulatum is one of the species with a long branchial 

 sac and numerous stigmata. 



The first detailed account of the structure of the genus Doliolum was given by 

 Huxley^ in 1851, when he described under the name of Doliolum denticulatum, Quoy 



1 Voyage de 1' Astrolabe, Zool. torn. iii. p. 599. 



2 Beschr. ein. neii. Moll. u. Zooph., Acad. Cces. Leop., Nova Acta, Bd. xi. pt. 2, p. 313. 

 ^ Remarks upon Appendioularia and Doliolum, Phil. Trans. 1851, part ii. p. 599. 



