THE MEDUSA. 139 
and it is from this animal in this state that those offspring come 
which have sexual distinction, that is, which are perfect animals. 
These two modes.-of propagation, so different, follow each other 
in a regular manner, and form a combination which has received 
the name of alternate gencration, a generation in which the children 
never resemble the parent, but always the grand-parent. ‘These 
neuter individuals which produce perfect creatures are called nwrses, 
a term not very happily chosen. These successive transformations 
which take place in the same animals appear at first sight very 
extraordinary, and yet similar phenomena are taking place every 
day around us, and we scarcely give to them any attention, either 
because the creatures are so common, or else it is that the changes 
MEDUSA LARVA. 
are of such frequent occurrence. For instance, the beautiful flutter- 
ing butterflies deposit eggs which lie immovable and helpless, and 
which have neither beauty nor elegance. These eggs, in due time, 
give birth to caterpillars which are destined to crawl with difficulty, 
and which are coated generally in sombre hues. In their turn the 
caterpillars change, and the brown mummy chrysalis is condemned 
to a death-like slumber, until it awakes into the richly-tinted 
butterfly which flits from flower to flower. If now these insects 
were excessively rare, and inhabited the ocean depths, would it not 
be a long time before we learnt that the eggs, and the caterpillar, 
and the chrysalis, and the butterfly, were the same animal in 
different phases of its being? And if this insect had an organi- 
sation less complete, perhaps the caterpillar, or the chrysalis, or 
even the egg, might have produced offspring by germination or 
55’ 
fissiparism ; that is, by buds, or by dividing its own body into 
