64 
LIFE, IN ITS LOWER FORMS. 
That order is briefly as follows : — The Polype, a fixed and 
rooted animal, increases its own individual life for a while 
by putting forth a succession of budding heads, but at a 
certain period gives birth to a number of beings that bear 
no resemblance to itself in form or habit, but are, to all 
ntents and purposes, free swimming Medusas. Each of 
these, after pursuing its giddy course for a time, produces 
a number of eggs, which change into active animals having 
the closest resemblance to Infusoria. Each of these latter 
presently becomes stationary, and affixed to some foreign 
body, along which it creeps, as a root-thread, shooting up 
tubular and celled Polypes, as described in the early part 
of this chapter. 
It is evident that this is a very different thing from the 
metamorphosis which takes place in Insects and Crustacea, 
where it is but one individual passing through a succession 
of forms, by casting off a succession of garments that con- 
cealed, and, as it were, masked the ultimate form. The 
butterfly is actually contained within the caterpillar, and 
can be demonstrated there by a skilful anatomist. In this 
case, however, there are distinct births, producing in a 
definite order beings of two forms, the one never producing 
its imago directly, but only with the interposition of a 
generation widely diverse from it. Hence, to use the 
striking though homely illustration of one of the first 
propounders of this law, any one individual is not at all 
like its mother or its daughter, but exactly resembles its 
grandmother or its granddaughter. 
