T6Ss LIVERPOOL BIOLOGICAL SOCIETY. 
of rather mysterious character, which are generally men- 
tioned in connection with the nervous system, namely 
Semper’s organ and the pedal gland. MRolleston, in his 
“Forms of Animal Life,” gives a dissection of Limaz 
flavus, and there he figures on the right side of the buccal 
mass the so-called ‘‘Semper’s organ.” In the explanation 
of the plate, Rolleston says: ‘‘ Semper’s organ is a 
structure consisting of cells like those of the salivary 
eland, but it is devoid of a duct, and very richly supplied 
with nerves from the supra-cesophageal mass, and supposed 
by its discoverer to be, possibly, an olfactory organ.” 
Then Rolleston refers to Semper (9), and adds: ‘‘It is 
large in Limaces, though small in the other air-breathing 
Gastropoda.”’ 
I dissected several specimens of Limaz agrestis, to 
find Semper’s organ, following the directions given by 
Rolleston, but I was not able to detect it. Thus I came 
to the conclusion that either Semper’s organ has a different 
structure and position in Limaz agrestis from what it has 
in Limaxz flavus, or what seemed more probable, that the 
description of Rolleston or Semper might be incorrect. 
When I looked for further information into the works of 
Claus (1), Gegenbaur (8), Huxley (4), Lankester (5), 
O. Schmidt (10), I found no further mention of the organ. 
But finally I met with references to it in the ‘‘ Zoologische 
Jahresbericht,’’ for 1880, part ili., and 1883, part 11. The 
one of the two papers in which Semper’s organ was men- 
tioned is written by Sarasin (49), the other by Sochaczewer 
(52). As I have not yet been able to get the original 
papers, I must be contented with the extracts given in the 
‘“‘Jahresbericht.’’ The extract of Sarasin’s paper is (trans- 
lated into English): ‘‘The author (Sarasin) examined the 
region of the mouth in the Pulmonata, and found a 
subepithelial ganglion inthe lips of the Helices. This 
