108 TUNICATA—SALPIANS CHAP. 
tail found in the larval condition of most Ascidians. The develop- 
ment is direct; and it may be said, then, that this young asexual 
(solitary) Salpa differs from the corresponding form in the life- 
history of Doliolum (Fig. 60, A) in that its tail is no longer a 
locomotory organ, but is represented by a nutritive mass, the 
elaeoblast, while the body, in place of being free, is attached by its 
ventral surface to a special organ of nutrition—the “ placenta ” 
—in connexion with the blood-stream of the parent. 
This embryo sexually produced inside the body of an aggre- 
gated form becomes a solitary Sa/pa (such as Fig. 61, B), which 
differs in appearance, structure, and habits from its parent, and 
has no reproductive organs. After swimming for a time, how- 
ever, it develops the ventral stolon on which buds form which are 
eventually sexual Salpae. These are set free from the solitary 
form in sets, still connected together, and they may swim about 
together for a time as a chain of aggregated Salpae before separating 
to become the adult sexual individuals (such as Fig. 61, A). 
Classification. —Salpa may be divided into the following sub- 
genera : '—Cyclosalpa, Blainville, in which the alimentary canal is 
ortho-enteric, and the “ chain” consists of individuals united in a 
circle ; Jasis, Savigny, with several embryos formed at a time; and 
Pegea, Sav., Thalia, Blumenbach, and Salpa, Forskal, all with 
one embryo only, and differing from one another in the condition 
of the “ gill” and other details: all except Cyclosalpa have the 
alimentary canal caryo-enteric. Cyclosalpa has three species, the 
best known of which is C. pinnata of the Mediterranean, a form 
possessing light-producing organs like those of Pyrosoma, but 
placed along the sides of the body. Salpa has four or five species, 
one of which, S. runcinata-fusiformis (Fig. 61), has occasionally 
been found in British seas; Zhalia includes the species 7. 
democratica-mucronata, which has been sometimes obtained in 
swarms in the Hebridean seas, or cast ashore on our southern or 
western coasts; Pegea has the species P. scutigera-confoederata ; 
and Jasis contains the remaining half-dozen species, the best 
known of which is L. cordiformis-zonaria, the only other Salpian 
which has been found in British seas. 
The family OcTACNEMIDAE includes the single remarkable 
1 For a more detailed account of these subdivisions of the Salpidae, and other 
groups, see Herdman’s ‘‘ Revised Classification of Tunicata,” Journ. Linn. Soc., 
Zool., xxiii. 1891, p. 558. 
