DEVELOPMENT. 207 
up into separate segments, which are, in fact, so many dis: 
tinct animals; and each turning over as it is set free, so 
as to bring the mouth below, develops into an adult Me- 
dusa, becoming more and more convex, and furnished 
with tentacles, circular canals, and other organs exactly 
like those of the progenitor that laid the original egg. 
Here we see a Medusa producing eggs which develop 
into Infusoria-like larvae, and these grow into stationary 
Fic. 174.—Alternate Generation: a, b, c, ova of an Acaleph (Chrysaora) ; d, e, f, Hy- 
dras; g,h, Hydras with constrictions; 7, Hydra undergoing fission; &, one of the 
separated segments, a free Medusa. 
forms resembling Hydras. The Hydras then produce not 
only Meduse by budding in the manner described, but 
also other Hydras like themselves by budding and by 
egos. All these intermediate forms are transient states 
of the Jelly-fish ; but the metamorphoses can not be said 
to occur in the same individual. While a Caterpillar de- 
comes a Butterfly, this Hydra-like individual produces a 
number of Meduse. Alternate generation is almost con- 
. fined to the low Radiates (Fig. 190). 
3. Growth and Repair. 
Growth is increase of bulk, as Development is increase 
of structure. It occurs whenever the process of repair 
exceeds that of waste, or when new material is added 
faster than the tissues are destroyed. There is a specitic 
