REPORT ON THE NUDIBRANCHIATA. 
13 
The most conspicuous external character of this genus consists in the armlike lateral 
prolongations of the anterior part of the body, which are especially developed in Glaucilla. 
Of these arms there are two pairs, the anterior being much stronger than the posterior. 
Sometimes the rudiment of a third pair is visible in a small cushion-shaped prominence. 
On the outer part of these arms are situated the papillae, generally in a single series, but 
sometimes ( Glaucilla ) in several series. In addition to these three groups of papillae 
there is, at any rate in large specimens, a fourth series. This is probably to be found in 
all the species of Glaucus, though only three groups have been described by several 
authors. The papillae are long and conical in shape, and become easily detached from the 
body. The body terminates in a long thin tail. The rhinophoria, which have a simple 
conical shape, are but slightly developed ; the conical tentacles are small. The foot is 
rather narrow ; the anterior extremity is truncated and rounded with very slightly 
prominent edges. 1 The genital aperture is situated behind the first arm, and the anus 
behind the second, slightly anterior is the opening of the renal organ. 
The colour of these animals is remarkable. The under side of the body as well as of 
the papillae is a fine ultramarine blue ; the upper surface is greyish but with a more or 
less strongly marked silver tint, which is also visible on the under surface. According to 
the observations of Reinhardt, made during the “Galathea” Expedition, this silver colour 
disappears when the animals are removed from the influence of sunlight. 2 
In the form of its jaws Glaucus differs from all other iEolidiadm ; they show a double 
convexity, and at the upper part are continuous with a horizontal plate. The radula 
only contains a single series of teeth, which are of the usual form with a prominent point, 
and on either side a series of strong denticles. 
Unlike what is found in most other AEolidiadse [pleuroproctce) , the common bile duct 
(the prolongation of stomach) lies beneath instead of above the hermaphrodite gland, 
as also in the Tetliydce, Dendronotidce , Dotidce, and Proctonotidce. The papillae dorsales 
are always provided with an urticating apparatus. The penis is always very strong and 
curved, and in the proper Glauci, armed with a strong curved hook. 
These animals inhabit the warmer parts of all the open seas, extending as far as 35° 
or 36° on either side of the equator, but rarely beyond. 3 
According to the observations of several naturalists (Chamisso, Eisenhardt, d’Orbigny, 4 
Reinhardt 6 ), their movements are but slow, hence the old name of “ Lacertse marinse ” 
would appear to be somewhat inappropriate. Bennett, however (Proc. Zool. Soc., iv., 1836, 
1 The foot, therefore, is rather well developed, and it is not easy to understand how Lesson (Voy. de la Coquille, Zool., 
t. ii. p. 286) could have written — “ Le pied est nul k moins qu’ on ne prenne pas pour rudiment de pied la ligne 
moyenne argentee qui suit toute la longueur du ventre.” 
2 Bergh, K. Dansk. Vidensk. Selsk. Skrif. R. 5, Bd. vii., 1864, pp. 247-248. Bennett (Proc. Zool. Soc., vol. iv., 1836, 
p. 117) mentions the rapidity with which these animals change their colours when dying. 
3 Bergh, loc. cit., pp. 249, 254. 4 Voy. aux lies Canaries, p. 42. 5 Bergh, loc. cit., p. 249. 
