35 
like a standard, over its head. The soft cicada spu- 
maria is protected by its froth, the aphides are in- 
volved in their soft, cottony secretion. The slime 
which covers the caterpillars of the saw flies, ten- 
thredines, retains its humidity though exposed to 
the fiercest sun?.” 
Of the class Mollusca some of the most. known 
are nude and smooth, as several of the garden slugs; 
some are covered with shells of various degrees of 
hardness, and conspicuous for their spinous pro- 
cesses. The most remarkable of these are the echini, 
the crust of which, however, is not identical with 
the shelly covering of the true testacea. The star- 
fish have also a crustaceous, tuberculated skin, more 
or less rough and hard in different species: the ne- 
reis gigantea appears to be covered with long iri- 
descent hairs of great beauty: in the aphrodite acu- 
leata the bristles are arranged along the whole of 
the lateral surfaces of the body in about thirty-five 
transverse rows: the Medusa pulmo is of a gelatin- 
ous consistence, and throughout of glassy trans- 
parency. Analogous coverings of plants are amongst 
the most familiar of natural objects. The downy 
verbascum is contrasted with the smooth tulip and 
orchis, the bristly cactus with the crinum; the rug- 
ged coated ilex with the smooth birch, the elm with 
the beech; the white thorn, mespilus oxyacantha, 
with the euonymodus in the same hedge; the nettle 
and thistle with the harebell; the rosa spinosissima 
with its neighbour the honeysuckle. 
P Introduction to Entomology, vol. ii. p. 225 and 228. 
D2 
