698 CLASS XI. 
Ann. des Se. nat., 31éme Série, v1. 1846, Zoologie, pp. 110—131. HUXLEY 
Observations upon the Anatomy and Physiology of Salpa and Pyrosoma. Phil. 
Trans. 1851, Pt. 11. p. 567. 
The species of Salpw are very generally dispersed ; sometimes 
they are met with in incredible quantities together ; notwithstand- 
ing, these animals a century ago were entirely unknown. The first 
announcement of them was made by P. Brown in his Civil and 
Natural History of Jamaica, published in 1756, under the name of 
Thalia; afterwards followed the description of the species observed 
in the Mediterranean and Red Sea, under that of Salpa by the 
Danish traveller Forskau'. Bosc and Cuvier next pointed out 
the resemblance of these animal species, described under two differ- 
ent names, which ought to be referred to the self-same genus. 
The body has an aperture at each extremity, but these apertures 
have a different form. The one is broad and transverse, and presents 
a valvular membrane, inasmuch as one of its margins is reflected 
inwards. The valvular membrane prevents the efflux of the water, 
which flows inwards by this opening and which is expelled by the 
opposite one from the contraction of the body. This expulsion of the 
water is the means by which the animal moves, so that the narrower 
opening is turned backwards. Cuvier thought that this opening 
was the anterior, and that thus the animal moved backwards. 
Since, however, the stream of water conducts also the food, and 
since in the Ascidiw the entrance to the cesophagus is situated 
behind in the respiratory sac, the common opinion, that the broad 
opening is the anterior, deserves to be preferred to this idea. The 
intestinal canal is situated on the outside of the respiratory cavity, 
in the space intervening between the external and internal covering, 
but terminates by both its apertures in the respiratory cavity. 
These animals, according to the testimony of Péron, TruEstvus, 
MeveEn and others, are usually phosphorescent by night. The Salpe 
are met with at one time singly, as distinct individuals, at another, 
united either in rings or in long chains, of which the arrangement 
is various, yet similar in individuals of one and the same species. 
These are attached to each other by tubercles or prolongations. 
CuHAmisso, from his observations on living animals, arrived at 
the conclusion, that successively a generation of distinct Salpe 
alternates with that of Salpew connected, and forming a chain. 
Thus a metamorphosis occurs, which, however, does not take place 
1 BrucurbRE, who gave in the Encycl. méthod. an extract from the descriptions of 
Forsk., changed the name Salpa into Biphora, which has found no general acceptance. 
