Experiments on the Development of the Livcr-Jluke. 
9 
removed from the Limax agrestis, and prefixed to the curious 
name "Arion fuscus, Miill." 
It is difficult to understand how the late Dr. O. A. L. Morch 
can have come, in 1875, to alter his previous entry in this 
manner. For the name "Arion" was unknown to Miiller, the 
author of the ' Historia Vermium,' having been introduced into 
malacology by Ferussac, as he himself tells us ;* and as regards 
the animal itself, on the supposition that Dr. Morch, by his 
entry " Arion fuscus, Miill.," intended to have written " Limax 
fuscus, Miill. ;" and knowing that this Limax, so called by 
Miiller, was really an Arion (Jiortensis^, and not a slug with a 
posteriorly placed respiratory inlet and a continuous shell, it 
is still more difficult to see how he could have added the word 
L. agrestis, L., apparently as a synonym. For in the thirteenth 
edition of the ' Systema Naturae,' tom. i. pars vi. pp. 3101— 
3102, the (true) '■^ Limax agrestis" is distinguished from the 
Limax fuscus" = Arion hortensis hodie) of "Miiller, 'Hist. 
Verm.' ii. p. ii. n. 209." 
On referring to Dr. O. A. L, Morch's " Faunula Mollus- 
corum Islandiae," communicated on the 13th April of 1866, and 
published in 1868, in Danish, in the ' Vidensk. Medd. fra den 
naturhist. Forening i. Kbvn,' pp. 185-227, I find at p. 196, 3, 
that " Limax agrestis, L." stands with a ? after its name, even 
though there can be no doubt from references to Olafsen, several 
of which are, in fact, given by Morch, that a grey slug, as well 
as the black slug, Arion ater, exists in Iceland. And a sugges- 
tion at the end of the entry, to the effect that the specimens 
may possibly belong to the species Limax tenellus, appears to 
explain the presence at the beginning of it of a ? after the 
words Limax agrestis. 
Perhaps, therefore, the true explanation of the entry in the 
Manual of 1875 is as follows. In the interval between 1857 
and 1875 a black slug may have been proved to Dr. Morch's 
satisfaction to have been found in Greenland, and he may have 
identified it as the Arion fuscus of Moquin-Tandon, which is the 
same as the Arion hortensis of Ferussac, and as the Limax fuscus 
of Miiller and Linnaeus ; and he may, by a very slight slip, 
have entered it as Arion fuscus, Miill.," instead of Arion 
fuscus, Moquin-Tandon," or " Limax fuscus, Miill." To his 
addition " Probably introduced," some objection might be taken 
on the ground that there is no very strong a priori reason why 
an Arion should not exist in Greenland, considering that it 
exists in Iceland, the land shells of which Morch himself f 
♦ 'Hist. Xat. des Mollusques,' ii. 1820-1851, pp. 23 and 54. 
t See Manual, p. 135. 
