10 Experiments on the Development of the Liver-Jluhe. 
allows are nearly allied to those of Greenland, and is not only 
an acknowledged member of the circumpolar fauna,* but the 
most abundant of all slugs in Finmark and Lapland. It is 
curious — and not only curious, but in view of the question 
of the distribution of Fasciola hepatica also important — to note 
what follows. In 1875 Dr. Moich appears, after thus adding 
Arion liortensis to his former list of Greenland mollusca, to have 
been content to leave the entry of " Limax agrestis, L., accord- 
ing to Wormskiold," untouched, though in smaller type, feeling, 
probably, that as the entry of the animal was overtly made only 
on the authority of Wormskiold, he was in no way pledged 
either to holding that it was Limax agrcstis, and not Limax 
tenellus, which existed in Greenland, or, indeed, to holding that 
any Limax whatever existed there. What completes my case is 
the fact that in 1877, when preparing a list of the Greenland 
mollusca for the English translation of Dr. Rink's ' Grijnland, 
of 1857, Dr. Morch omits all mention of Limax agrestis alto- 
gether, and his entry runs as follows (p. 436) : — 
"Class i. ANDROGYNA. 
Order i. Geophila, Fer. 
1. Arion fuscus. Probably introduced." 
If we follow Dr. Mbrch, therefore, we shall strike Limax 
agrestis out of the list of Greenland mollusca, and hold that 
Arion liortensis, which exceeds it in number in other circum- 
polar regions, has in Greenland displaced, or at any rate 
replaced, it altogether. 
If, however, Limax agrestis, notwithstanding the advantage 
which its coloration might be supposed to have been likely to 
give it, is beaten in the struggle for existence in circumpolar 
districts by Arion liortensis, of about the same size, but of such 
different colour in other districts, if not in the North,! not 
* Middendorff, indeed, in his ' Sibirische Reise,' ii. 1851, p. 419, omits the 
name of this small slug from his list of Circumpolar Freshwater and Land 
Molluscs, but five pages farther on, I.e., says in a note, " Vielleicht ist Limax 
(Arion) suh-fuscus, Drap. (Drap. ' Moll.' p. 125, pi. ix. 8 ; Limax fasciatm, Nillsen, 
'Hist. Moll. Suec' 1822, p. 3) cine circumpolare Art dieses Geschlechtcs ;" and 
he proceeds to note its discovery by himself within the polar circle in Finland, 
feeding on sphagnum, as also in Lapland, feeding on fungi, up to 69° N. Lat. 
Schrenk (' Reise in Amurlande,' 1859-1867, ii. p. 692), whilst identifying the 
Limax suh-fuscus of Draparnaud with the Arion liortensis of Fe'russac, and so with 
the Limax fuscus of MUller and Linnwus, confirniS the view as to its circum- 
polar character, and uses it as an argument for its being indigenous in America. 
t Even in England, where the Arion liortensis is often of a " deep blue-black," 
and is, I suspect, the " Black Jack " of agriculturists; it is not rarely " yellowish, 
sometimes gray or greenish-gray. ' — (Lovell Reeve's British Land and Fresh- 
water Molluscs, p. 11;. In Amoorland it is '' graugelblich," with three stripes, 
one dorsal and two lateral narrower ones ; whilst its rival the Limax agrestis is 
described as " hell-braunlich- oder bliiulich-grau." — See Schrenk, I.e. 
