14 
THE VOYAGE OF H.M.S. CHALLENGER. 
p. 118), remarks on the great mobility of the tail, which may possibly have suggested a 
comparison with the tail of a Lizard to the older naturalists. They appear never to swim 
actively about, but merely to float on the surface of the sea with the foot uppermost, the 
papillae serving as “balancers.” 1 According to Bory de St. Vincent and Forster 2 this 
position is sometimes reversed, but Reinhardt did not observe this. These animals take 
in and expel air through the mouth (Forster, Bennett, Reinhardt), and Reinhardt 3 states 
that immediately after the expulsion of air-bubbles, a bluish fluid, not readily soluble in 
sea water, is evacuated. This fact is also noticed by Forster 4 and Bennett f the latter, 
however, describes the fluid as brownish in colour, and regards it as being of a foecal nature. 
In the specimens of Glaucus which I examined, there was nearly always a quantity 
of air in the stomach, which was readily expelled from the mouth, together with a 
violet-coloured liquid, on applying a slight pressure to the back of the animal. The 
contractility of the body and its appendages is very great, and accounts for the 
differences that exist in the figures given by various authors. The papillae of the body 
are readily detached, as in many other iEolidiadae. According to Forster, 6 this is 
also the case with the tail ; I very rarely saw an individual, however, that was without 
a tail. 
According to Vayssiere, Glaucus is phosphorescent. Its food appears to consist 
chiefly of V della and Porpita. 1 Quoy and Gai m ard 8 were the first to give a description 
of the spawn of Glaucus ; it has since been figured and described by Souleyet, 9 and 
by myself. 10 D’Orbigny 11 states that the spawn is deposited upon the disc of Velella. 
Copulation has been observed and described by cl’Orbigny and Lesson, 12 and I have myself 13 
noticed individuals which appeared to be in the act of copulation. The development is 
up to the present quite unknown. 
When preserved in alcohol, these animals become very much altered in shape, and 
for this reason very different accounts have been given of the number of species which 
exist. Most observers who have seen the living animals, distinguish several species 
(Rang 2, Eschscholtz and Reinhardt 4, Lesson 6) ; those, on the other hand, who have 
1 The assertions of some naturalists that Glaucus is able to swim by means of the “ gills ” were denied by Chamisso 
and Eisenhardt (Nov. Act. Nat. Cur., X., 1821, p. 347), as well as by Eschscholtz (Zool. Atl., Heft 4, 1831, p. 16). The state- 
ment of the last-mentioned author that the animal swims by means of air-bubbles under the “ventral disc” ( loc . cit. 
and Isis, 1825, I. col. 737) means really that it is kept floating at the surface of the water by help of the swallowed 
air. A. Adams (Ann. and Mag. Nat. Hist., ser. 2, vol. xix., 1857, p. 462) appears to have noticed this habit of 
swallowing air, and Forster many years ago (Voigt, Magazin, loc. cit., p. 361) saw the expulsion of air-bubbles through 
the mouth (“ per os spirant ”). 
2 Voy. de la Coquille, t. ii. p. 284. Voy. aux quatres lies d’Afrique, I., p. 136, pi. vi. fig. 1, a.b. Voigt, Magazin, 
&c , loc. cit., p. 341. 
3 Bergh, loc. cit., p. 250. 4 Voigt, Magazin, &c., Bd. v., 1803, p. 341. 5 Loc. cit., p. 115. 
6 Voigt, Magazin, &c., p. 341. 7 Bennett, loc. cit., pp. 113-119 ; Bergh, loc. cit., p. 251. 8 Loc. cit., p. 279. 
8 Voyage de la Bonite, p. 442, pi. xxiv. fig. 25. 
10 Bergh, loc. cit., pp. 281, 291, 293, 298, 302, Taf. vii. fig. 18. In Gray’s Figures of Molluscous Animals (vol. iii. 
pi. cci. fig. 6a) the spawn is not well represented (after a drawing of Hooker ?). 
11 Voy. aux lies Canaries, p. 42. 12 Loc. cit., pp. 280, 287. 13 Bergh, loc. cit., p. 282, Taf. vii. fig. 14. 
