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Page 11
We now approach the most extraordinary portion of the history of
these creatures. Recent investigations have brought to light the most
interesting facts respecting their reproduction and development. It is
now known that the young jelly-fish passes through a series of
transformations before reaching its perfect state.
At certain seasons, eggs are produced within the body of the parent in
appropriate ovaries, where they are retained for a time. They are then
transferred to a kind of marsupial pouch, analogous to that of the
kangaroo, where their development proceeds. After passing through
certain changes here, the egg issues from the maternal pouch as an
oval body, clothed with cilia--an animalcule in external aspect, and
as unlike its parent as can well be imagined. For awhile the little
creature dances freely through the water, and leads a gay, roving
life; but at last it prepares to 'settle;' selects a fitting locality;
applies one extremity of its body to the surface of stone or weed, and
becomes attached. And now another change passes over it. The cilia, no
longer needed, disappear. A mouth is developed at the upper extremity
of the body, furnished with a number of arms. Gradually this number
increases, and the jelly-fish now appears in the disguise of a polype,
which feeds voraciously on the members of the class from which it has
itself so lately emerged. At this point there is a halt. The medusa
remains in its polype state for some months. At the expiration of this
term, a strange alteration in its appearance begins to take place.
Rings are formed round its body, from ten to fifteen in number. These
gradually deepen, until at length it is literally cut up into a number
of segments, which rest one upon the other--their upper margins
becoming elevated, and divided into eight lobes. It is, in fact, a
pile of cup-shaped pieces, very loosely connected together. A little
later, these pieces free themselves successively, and the sedate
polype disappears in a company of sprightly young medus�. These
beings, indeed, still differ in some respects from the adult animal;
but the differences gradually vanish, and we have the perfect
jelly-fish as the final result of this extraordinary series of
transformations.
Similar observations have been made respecting other tribes amongst
the lower animals, and some interesting generalisations have been
founded upon them, into which, however, it is not our present purpose
to enter.
The _Acaleph�_ are the principal agents concerned in the production of
the beautiful phenomena of phosphorescence. The minute species--mere
gelatinous specks--swarm at times by countless myriads in the waters
of the ocean, and make its surface glow with 'vitalised fire.' The
waves, as they curl and break, sparkle and flash forth light, and the
track of the moving ship is marked by a lustrous line. 'In the torrid
zones between the tropics,' says Humboldt, 'the ocean simultaneously
develops light over a space of many thousand square miles. Here the
magical effect of light is owing to the forces of organic nature.
Foaming with light, the eddying waves flash in phosphorent sparks over
the wide expanse of waters, where every scintillation is the vital
manifestation of an invisible animal world.' Beneath the surface
larger forms are seen, brilliantly illuminated, and lighting up the
mystic depths of the sea. Fiery balls and flaming ribbons shoot past;
and submarine moons shine with a soft and steady light amidst the
crowds of meteors. 'While sailing a little south of the Plata on one
very dark night,' says Mr Darwin, 'the sea presented a wonderful and
most beautiful spectacle. There was a fresh breeze; and every part of
the surface, which during the day is seen as foam, now glowed with a
pale light. The vessel drove before her bows two billows of liquid
phosphorus, and in her wake she was followed by a milky train. As far
as the eye reached, the crest of every wave was bright; and the sky
above the, horizon, from the reflected glare of these livid flames,
was not so utterly obscure as over the vault of the heavens.' Even in
our own seas very beautiful displays of phosphorescence may be
witnessed. On fine summer nights, a soft, tender light plays round the
boat as it moves onward, and the oars drop liquid fire. For how much
of beauty are we indebted to these living specks of jelly?
Of the extreme minuteness of some of the species, an idea may be
formed from the fact, that 110,000 might be contained in a cubic foot
of water. We can say nothing with certainty as to the cause of the
phosphorescence of the medus�, and shall not trouble our readers with
mere speculations.
The jelly-fishes furnish us with a striking illustration of the
profusion of life in the ocean. Provision has indeed been made for
securing in all the realms of our globe the largest possible amount of
sentient being, and consequently of happiness. And to each tribe a
definite part is assigned--a special mission is intrusted. None can be
spared from the economy of nature. The shoals of microscopic medus�
store up in their own tissues the minute portions of nutritious matter
diffused through the waters, and supply food for the support of higher
organisms. All the tribes of animated beings are dependent one upon
another. That the greatest may enjoy its existence and fulfil its
work, the least must hold its place and discharge its function. They
co-operate unconsciously to secure the unity and harmony of a system
which is designed to promote alike the interests of each and all of
them.
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