Tol 
warmth and moisture that is provided they are liable to 
multiply exceedingly. Experiments carried out at the 
Rothamsted Station have shown that we can very con- 
siderably reduce this undesirable population by partial 
sterilization of the soil by means of steam. In cases of 
very bad infestations of Eelworm this method is said to 
be the only effective remedy at present available. 
SLUGS and SNAILS (6), (7), belong to the class of the 
Mollusca, which is a large assemblage of animals includ- 
ing such divers forms as Oysters, Whelks, Scallops, Octopi, 
and the familiar fossils which are known as Ammonites 
and Belemnites. Both Slugs and Snails differ from other 
Molluscs in being land and not aquatic animals. They 
are always provided with a pulmonary chamber, which is 
a kind of lung enabling them to breathe in the air. In 
aquatic Molluscs this pulmonary chamber is almost always 
absent, respiration taking place by other means. 
SNAILS or Helicidz are provided with an external 
spiral shell into which the animal can withdraw itself, and 
ere are three species which are commonly met with. The 
Garden Snail (Helix aspersa, Mull.) is the largest and 
its shell: measures about 14 inches in diameter. It is well 
enough known to need no description, being easily recog- 
nisable by its brown shell marked with pale irregular 
lines. The Strawberry Snail (47. rufescens, Pen.) has a 
shell which seldom exceeds half an inch in diameter and 
is more flattened in form. It also varies in colour from 
dirty grey to brown or reddish-brown, often with a num- 
ber of transverse streaks of a darker tint. The Wood 
Snail (H. nemoralis).has an extremely variable shell being 
white, grey, pinkish, yellow or brown, and is marked with 
one to five or more conspicuous brown spiral bands. It 
is, moreover, considerably larger than the Strawberry 
Snail. 
SLuGsS or Limacide are naked and only possess a 
vestigal shell, which is placed near the hinder end of the 
‘body or buried beneath the skin of the back; all the 
injurious species have the shell in the latter position. The 
situation of the shell is clearly marked externally and 
the area of skin covering it is known as the shield or 
mantle. Closely related to the margin of the latter, on 
the right side of the body, is the respiratory pore—a well- 
defined aperture leading into the pulmonary chamber. 
Slugs secrete an abundance of mucous, which serves to 
