TUNICATA. 705 
the name of Ascidiwm (Natuurk. Uitspanningen, 1. bl. 97), and 
Linnavs, in the twelfth edition of his Systema Nature, changed 
this name, without any reason that I am aware of, into Ascidia. 
These Ascidie or bag-pipes (zakpijpen), as BAsTer names them, 
are always attached to other bodies, to rocks, shells, crabs, &c. Often 
several individuals are united in a single group; they never, how- 
ever, form such a compound body as the preceding genera, which 
are distinguished by the orificia analia being always turned towards 
each other, and more or less really united, (Savieny, op. cit. p. 120), 
whilst the external covering is common to all the individuals that 
combine to form the group. 
These animals ingurge water through the branchial aperture, and 
eject it chiefly by the same aperture in jets, which may serve as 
a defensive means for chasing animals away that attack them. 
Cuvier asserts that the expulsion of water can be performed 
through the branchial aperture alone. Those writers, however, who 
have observed them alive, are unanimous in their testimony that the 
ejection of water is effected through both apertures. Carus tells, 
that in a large specimen of Ascidia microcosmus he saw an opening 
furnished with a membranous valve, which appeared to lead from 
the branchial sac to the porus analis. Other writers, however, do 
not speak of such an opening. On the supposition of Lister and 
Mitye Epwarps that the branchial sac is perforated like a sieve 
(see above, p. 693), the matter may be explained without difficulty. 
Whether Ascidians also ingurge water by the cloacal aperture after 
a vacuum in the gill-sac has been caused by contraction, as SAVIGNY 
suspected (op. cit. p. 100), deserves further investigation. 
Ascidians live on small organic particles, which are brought with 
the water into the respiratory sac and thence to the esophagus that 
opens at its bottom. Sometimes, indeed, small crustaceans have 
been found in the sac, but they would seem to have arrived there 
fortuitously ; for when they have been ingurged by an Ascidian they 
are rather hurtful than beneficial, and in some cases even injure the 
tissue of the gills. 
EYSENHARDT has published observations from which it appears that the 
body of Ascidians in a singular manner may change into a formless mass, 
on which other Ascidians attach themselves, and take root. Nov. Act. 
Acad. Ces. Leop. Carol. Vol. X1. 1823, pp. 249—272. 
Comp. also on these animals (besides the works of Cuvier, SAvieny and 
Vawn BENEDEN already cited) Carus Bettrdge zur Anatomie und Physiologie 
der Seescheiden, in MucKEL’s Arch. f. die Physiol. 11. 1816, s. 569—590 
VOL. I. AB 
