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98 THE AUSTRALIAN NATURALIST. 
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Snails crawling ov plain brown linoleum leave a very 
clear intermittent® trail, the waxy surface of the linoleum | 
not lending itself to the spreading of the mucus as glass 
does, and thus tending to preserve intact the separate de- 
posits. When a snail is crawling on glass the muscular 
motion of its foot or sole is very clearly seen from beneath, 
passing forward in a series of simultaneous waves like those 
seen in the legs of a crawling myriapod. The tracks of 
slugs, Lima, ete., closely resemble those of snails, but on a 
smaller scale, and the bridging from one deposit to another, 
on rough surfaces, is usually more complete. 
Both snails and slugs secrete two kinds of mucus, apart 
from that secreted by the genital gland. That forming the 
track is, as has been mentioned, the product of the large 
ventral mucus gland. In both cases it is a clear, glairy, 
very tenacious substance. When the animal is crawling 
quietly, without being disturbed, the mucus is quite trans- 
lucent, and under the microscope shows only a few scattered 
rounded cells and some nucleated cells, which I suppose 
to be epithelium cells. As a distinctive term, I would pro- 
pose to call this secretion the ambulacral mucus. On the 
ether hand, the secretion coating the dorsal surface, both 
of snails and slugs, and which may perhaps best be dis- 
tinguished by terming it dermal mucus, is turbid, and 
when examined microcopically is seen to be densely crowded 
with minute structurless granules or cells of varying dimen- 
sions, mostly sausage-shaped, and reminding one of a crowd 
of diatoms. When the animal is irritated, by touching or 
in other waysy the seeretion is poured out abundantly. It 
is the product of numerous epidermal glands, resembling 
those deseribed by Dr. A. Dendy in his description of the 
anatomy of a land planarian, Trans. Royal Soc., Victoria, 
1899 (See also Outlines of Zoology, by J. Arthur Thomson, 
1892 edition, pp. 319, 321). 5 
Sometimes, particularly when the animal is disturbed 
when crawling, the mucus of the track contains portions of 
the dermal mucus trailed off as the snail moves along. ‘The 
ambulacral mucus is frequently stained with streaks of 
yellow or green, through contamination with excrement. 
Snail mucus is not coagulated by boiling water, but is coagu- 
lated through dehydration, by alcohol. I have used the 
term ‘‘mucus’’ in referring to these secretions because I 
think it is a better term than slime, which is sometimes 
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