Experiments on the Development of the Liver-Jlulie. 11 
only to have been called fuscus and suh-fuscus, but even to have 
been confounded with the ime Arion atcr (from which, indeed, it 
is mainlj disiinguishcd bj its more mesially placed respiratory 
orifice and its small size) — it surpasses Avion hortensis * in more 
southern latitudes. 
Middendorff indeed expressly says, I.e. : " In Siberien traf 
ich diesen Limax (^Arion hortensis) nicht, sondern nur einen 
einzigen kleinen Limax in Starowoj Gebirge, welcher dem 
Limax a()restis, L. recht iihnlich sehe." But this absence from 
Siberia, to which F. Schmidt's silence as to its presence bears 
some testimony, may be paralleled by the similar absence of 
Paludina vivipara (Middendorff, I.e., p. 426) and of crayfishes 
from the Siberian river basins,t and, as in those two cases, when 
compared with the facts of a distribution elsewhere does not 
disprove a circumpolar character. 
Gerstfeldt, ' Me'm. Sav. Etrang. St. Petersbourg,' 1859, 515 
(11), refers to some few, small, ill-preserved specimens, 
" einige wenige kleine und schlecht erhaltene Exemplare " of 
slugs from Irkutsk and Wilni and from the Amur, and speaks 
of them under the name Arion ater. Their small size may 
justify us in supposing them to have been Arion hortensis ; and 
the bad state of preservation in which they were, and which 
makes Gerstfeldt himself speak doubtfully of his identification, 
p. 535 (31), makes this note of their presence less authoritative 
than it otherwise would have been, and has caused Schrenk to 
suggest that they were in reality specimens of Limax agrestis. 
An illustration of the paucity and rarity of Limax agrestis 
in circumpolar regions is furnished by the entry made by 
Frederich Schmidt in his list of Animals from the Region of the 
Lower Yenisei, ' Mem. Acad. St. Petersbourg,' 1872, p. 48, as to 
this eminently social mollusc : " In einem faulen Treibholzstamm 
auf den grossen Brjochow Insel (70° N. Br.) in einem Exemplar 
gefunden." But, per contra, in Amoorland, Schrenk tells us, 
I.e., that Limax agrestis outnumbers Arion hortensis, just as 
Arion hortensis outnumbers Limax agrestis in Sweden, Finland, 
and Lapland, and that while Limax agrestis spreads into Spain, 
Portugal, Italy, Algeria, and the southern slopes of the Caucasus, 
Arion hortensis reaches no farther south than the southern slopes 
of the Pyrenees and Alps. 
In a letter published in the 'Times' of April 14, 1880, 
and republished with certain omissions in the ' Zoologischer 
Anzeiger ' of May 24, p. 258-260, I suggested that Arion ater 
may be the Zicischenwirth," or one Zudschemcirth," to Fasciola 
* See Schrenk, ' Amurlande,' ii. 690-693, 1869. Middendorff, 'Sibirisclie 
Eeise,' ii. p. 424, 18,il. 
t See Huxley ' On Crayfishes,' p. 305. 
