60 PHYLUM TUNIC ATA (iJROCHORDA). 



tion incapable of budding. The budding form is often called 

 the " nurse, " ; its buds have three different fates according to 

 the time at which they are produced. The first formed buds 

 become nutritive individuals, called gastrozooids or tropho- 

 zooids, the next become phorozooids which act as foster- 

 mothers to the latest formed buds, which in their turn become 

 the fully developed sexual animal (gonozooid). 



The budding of Doliolum, in the early detachment and subsequent fission 

 of the buds, resembles that of the Distomidae. The fate of the five cell- 

 masses found in the young probud appears to be as follows. The atrial 

 outgrowths give rise to the nervous system and muscles, the pharyngeal 

 outgrowths to the pharynx, digestive tube, genital organs, and the meso- 

 derm mass to the pericardium. The atrium arises as a dorsal invagination 

 of ectoderm. 



Doliolum Quoy and Gaimard, 2 mm. to 3 cm. in length, in most warm 

 seas. The description of the sub-order applies to this genus. There are 

 two other genera, but in neither of them is the budding form known, and 

 our knowledge is in other respects imperfect. Anchinia Esch., known 

 only by fragments of the dorsal appendage of the nurse. The buds are 

 arranged without regularity on the dorsal appendage extending on to 

 the ventral surface ; the ventral are the oldest. The ventral stolon appears 

 to lie along the dorsal side of the proximal part of the dorsal appendage. 

 Three kinds of zooids are found upon different fragments of the dorsal 

 appendage, one of which is sexual ; the sexual form has 4 muscular hoops 

 and an S-shaped band on each side, 3-8 mm., Mediterranean. Dolchinia 

 Korotneff, known only by fragments of its dorsal appendage, on which no 

 remains of the ventral stolon have been found ; two kinds of zooids have 

 been found, the phorozooids and the sexual zooids ; they closely resemble 

 Doliolum and have 8 muscular hoops and a portion of a ninth ; both kinds 

 become detached and swim freely, Med., found only once (1891) at Naples, 

 and never since seen, 5 mm. 



Order 3. APPENDICULARIAE (PERENNICHORDATA,* 

 LARVACEA, COPELATA). 



Pelagic Tunicata of small size, with a persistent notochord and 

 only two gill-apertures. The gill-apertures and anus open directly 

 to the exterior. 



* Mertens, Beschreibung der Oikopleura, einer neuen molluskengatt- 

 ung, Mem. de VAcad. Petersbourg (6), 1, 1831, p. 205. J. Muller, Bericht 

 iiber einige neue Thierformen der Nordsee, Mutter's Arch., 1846-7. Hux- 

 ley, Remarks upon Appendicularia and Doliolum, Phil. Trans., 1851. 

 Id., Further observations on the structure of Appendicularia ftabellum, 

 Q.J.M.S., 4, 1856. Fol, Etudes sur les Appendiculaires du detroit de 

 Messine, Mem. de la Societe de Phys. et d'Hist. Nat. de Geneve, 21, 1872. 

 Chun, Die pelagische Thierwelt in grosseren Meerestiefen, etc. Biblioiheca 

 Zoologica, 1, 1888. 'Id., Ber. iib. eine nach Canarischen Inseln ausgefiihrte 

 Reise, Sitzb. K. pre.ua. Akad., 30, 1889, p. 547. Lohmann, Die Appendic- 

 ularien der Plankton-Expedition, Ergebnisse d. Plankton-Epedition d. 

 Humboldt-Stiftung, 2, 1896. Seeliger, Bronris Thierreich, op. cit. 



