1S8 
LECTURE XL 
Among the species of Lepas without the co- 
riaceous tube or stem, or such as are immediately 
affixed by the base of the shell, one of the most 
common is the Lepas Balanus of Linnaeus, or com- 
mon Acorn-Shell; frequently seen about almost 
all the European coasts, on rocks, &c. and a 
smaller species, extremely resembling it, is often 
seen grouped on the backs of Oyster-shells. The 
animals of the whale tribe are often infested by 
various kinds of Lepades, some of which are merely 
affixed to the surface, while others are deeply im- 
bedded, to the distance of some inches beneath the 
cuticle. 
Having thus given a general description of the 
testaceous tribe, we have to observe, that the shell- 
animals are produced from eggs, which in some 
species are gelatinous, and in others covered with 
a calcarious shell; and that the young animal 
emerges from the egg with its shell on its back : the 
most familiar and convincing proof of this may 
be obtained by observing the evolution or hatch- 
ing of the eggs of the common Garden Snail, as 
well as of several of the water-snails, which depo- 
sit eggs so transparent that the motions of the 
young, with the shell on its back, may be very dis- 
