Observations on the Mycophagous propensities of Slugs. 87 
Sense of Smell. 
The olfactory sense is very highly developed in the mollusca 
generally, and is of more value to them than sight. Most 
authorities regard this sense as being situate in the tentacles. 
Moquin-Tandon (1851) made experiments by removing the 
tentacles, and he was satisfied that the animal then lost this 
sense or nearly so. Sochaczewer (1881) located this sense in a 
pedal gland near the mouth. Simroth (1882) says that it is 
distributed over the entire soft integument, as well as being 
concentrated in the tentacles, and. near the respiratory orifice 
(Cooke, p. 192). Many experiments are recorded showing how 
acutely perceptive these animals are with the olfactory sense 
in the matter of food, but especially so with fungi. 
Buller (1922) recorded an interesting series of observations 
he had made with Limax maximus and Phallus impudicus. He 
observed that the former found its way back many times to 
the Phallus by its sense of smell, even when removed from it to 
a considerable distance. 
Blood and Nervous System. 
Molluscan blood generally is colourless and devoid of red 
corpuscles. Haemoglobin as found in the blood of vertebrates 
is not present except in a few cases, for mollusca do not require 
great facilities for oxidisation, since being otiose, it is not 
necessary for the oxygen to be generally diffused. Haemocyanin, 
an albuminoid containing copper, largely replaces this haemo- 
globin. Its functions are similar, but less effective. Haemo- 
globin, however, is present in the buccal tissues of some species, 
since this is a part where energetic action is called for, also white 
corpuscles or amoebocytes occur much resembling those found 
in man (see Cooke, p. 171). This variation in the composition 
of the blood, as compared with that of man, may account for 
the fact that phallin, a solvent of red blood corpuscles, an 
alkaloid which is found in fungi, and poisonous to man, has no 
toxic effect on slugs. Muscarin, also, another alkaloid present 
in fungi producing a toxic effect on man since it causes paresis 
of the heart’s action, is without effect on slugs because of their 
simpler nervous system; for these animals do not possess any- 
thing analogous to the sympathetic system in man which con- 
trols the heart’s action; or it may be, these alkaloids are not 
absorbed by the molluscan tissues, and pass out through the 
alimentary tract. 
The conclusions that may be deduced from these experiments 
below are: 
1. Avion ater, A. intermedius and Limas maximus are extremely 
