Glimpses of Ocean Life 5

Glimpses of Ocean Life 5

The motions of the Vorticella do not seem much affected by the stalk

losing hold of its attachment; but the result of such an accident

taking place is that the cilia cause the animal to swim through the

water, trailing its thread behind it, and the contraction of the latter

merely causes it to be drawn up to the head.

 

There are various species of Vorticellæ. That just described is the

simplest, consisting merely of a hemispherical ciliated cup, attached

to a single thread. It is barely visible to the naked eye. But there

is a compound species which I have this year found to be extremely

abundant in my aquarium,--whose occupants, both large and small, it

excels in singularity and beauty. In structure it is to the simple

Vorticella what a many-branched zoophyte is to an _Actinia_. My

attention was first drawn to the presence of this creature by observing

some pebbles and fronds of green ulva thickly coated with a fine

flocculent down. On closer inspection this growth appeared to consist

of a multitude of feathery plumes, about one-sixteenth of an inch in

height, and individually of so fine and transparent a texture as to be

scarcely discernible to the unassisted sight. On touching one with the

point of a fine needle it would instantly shrink up into a small but

dense mass, like a ball of white cotton--scarcely so large as a fine

grain of sand. In a few seconds it would again unfold and spread itself

out to its original size. By carefully detaching a specimen with the

point of a needle or pen-knife, and transferring it, along with a drop

of water upon a slip of glass, to the stage of the microscope, a sight

was presented of great wonder and loveliness:--

 

'The more I fixed mine eye,

Mine eye the more new wonders did espye!'

 

Let the reader imagine a tree with slender, gracefully curved, and

tapering branches thickly studded over with delicate flower-bells

in place of leaves. Let him suppose the bells to be shaped somewhat

between those of the fox-glove and convolvolus, and the stem, branches,

bells, and all, made of the purest crystal. Let him further conceive

every component part of this singular structure to be tremulous with

life-like motion, and he will have as correct an idea as words can give

of the complex form of this minute inhabitant of the deep. Moreover,

while gazing at it through the microscope, the observer is startled

by the sudden collapse of the entire structure. The lovely tree has

shrunk together into a dense ball, in which the branching stem lies

completely hidden among the flower-bells--themselves closed up into

little spherules, so closely packed together that the entire mass

resembles a piece of herring-roe. This contraction is so instantaneous

that the mode in which it is accomplished cannot be observed until the

tree is again extended. As the re-extension takes place very slowly, we

are enabled to observe that each branchlet has been coiled in a spiral

form, like the thread of the simple Vorticella previously described;

and also that the main stem, above the lowest branch, was coiled up in

the same way, but not so closely, and that the part below the lowest

branch had, curiously enough, remained straight. Sometimes, in large

and numerously branched specimens, one or two of the lowest members

do not contract at the same time with the rest, but do so immediately

afterwards, as if they had been startled by the shrinking movements of

their neighbours. Sometimes these lowest branches will contract alone,

while all the others remain fully extended,--a fact that would almost

seem to indicate that they possessed an independent life of their own.

 

In the accompanying engraving I have attempted faithfully to portray

one of these wonderful creatures. Fig. 1 represents it fully extended,

while Fig. 2 indicates its collapsed form. There is another curious

circumstance which I have fortunately observed in connection with this

Vorticella, a description of which will perhaps be interesting to the

reader. I allude to the casting off of what may be called the fruit

of the tree. When this event takes place, the buds (or fruit) dart

about with such rapidity, that it is almost impossible to keep them

in the field of view for the briefest space of time. A represents the

enchanted fruit hanging on the tree; B shows it as it swims about.

 

[Illustration: Fig. 1. and Fig. 2.]

 

Although not exactly fruit, it is, no doubt, the means by which

the Vorticellæ are propagated, for it is known that many fixed

zoophytes, and even some plants, produce free swimming germs or spores,

which afterwards become fixed, and grow up into forms like those

which produced them. In some of the branching zoophytes (_Coryne_,

_Sertularia_, &c.), the germs are exactly like little medusae, being

small, gelatinous cups fringed with tentacula, by means of which they

twitch themselves along with surprising agility. In this Vorticella,

however, it is more like one of the ciliated Infusoria. The first one

that I saw attached I conceived to be a remarkably large bell, with

its mouth directed towards me, but the cilia with which it appeared

to be fringed were unusually large and distinct. The movements of

these appendages being comparatively slow, it was most interesting

to watch them as they successively bent inwards and rose again, like

the steady swell of a tidal wave, or an eccentric movement in some

piece of machinery, making a revolution about twice in a second, and

in the opposite direction to the hands of a clock. Suddenly the tree

contracted, when, to my surprise, I observed the bell, which not an

instant before appeared attached, now floating freely in the water,

its ciliary movements not being in the least interrupted. Presently,

however, they became brisker, the bell turned over on its side, and,

ere the tree had again expanded, darted out of view, not, however,

before I had remarked that it was not a bell, but a sphere flattened

on one side, and having its circular ring of cilia on the flat side,

with only a slight depression in the middle of it. There also appeared

to be a small granular nucleus immediately above this depression, the

rest of the body being perfectly transparent. I afterwards saw several

others attached to the tree, each seated about the centre of a branch;

but none of these were so fully developed. They were like little

transparent button mushrooms, and had all more or less of a nucleus

on the side by which they were attached. On only one of these did I

detect any cilia.

 

Mr. Gosse, in his 'Tenby,' gives a picture of an animal exceedingly

like what I have described; but from his account of it, there seems to

be some doubt of their identity. He calls it '_Zoothamnium spirale_,'

because the insertions of the branches were placed spirally around the

main stem, like those of a fir-tree. In my specimens the branches were

set alternately on opposite sides of the main trunk, and the whole was

curved like a drooping fern leaf or an ostrich feather, the bells being

mostly set on the convex side.

 

In conclusion, let me mention that it is an error to suppose, as many

persons do, that putrid water alone contains life. Infusoria occur,

as before hinted, in the clear waters of the ocean, in the water that

we drink daily, and also in the limpid burn that flows through our

valleys, or trickles like a silver thread down the mountain side.[1]

 

[1] Ehrenberg states that Infusoria are in a higher state of

organization when taken from pure streams than from putrid waters.

 

'Where the pool

Stands mantled o'er with green, invisible,

Amid the floating verdure millions stray.

Each liquid too, whether it pierces, soothes,

Inflames, refreshes, or exalts the taste,

With various forms abounds. Nor is the stream

Of purest crystal, nor the lucid air,

Though one transparent vacancy it seems,

Void of their unseen people. These, concealed

By the kind art of forming Heaven, escape

The grosser eye of man.'

 

Let it be remembered, too, that Infusoria, when found in either do not

themselves constitute the impurity of fresh or salt water; they merely

act as 'nature's invisible scavengers,' whose duty it is to remove

all nuisances that may spring up; and most unceasingly do these tiny

creatures labour in the performance of their all-important mission of

usefulness.

 

 

 

 

CHAPTER III.

 

Sea Anemones.

 

 

'The living flower that, rooted to the rock,

Late from the thinner element,

Shrunk down within its purple stem to sleep,

Now feels the water, and again

Awakening, blossoms out

All its green anther-necks.'

 

 

 

 

[Illustration:

 

1 Sir J. G. Dalyell's celebrated ACTINIA (Drawn from Nature Jan. 1860.)

2 A. CRASSICORNIS

3 CAVE DWELLER (_A. troglodytes_)]

 

 

 

 

III.

 

 

No marine objects have become more universally popular of late years

than Sea Anemones. Certainly none better deserve the attention which

has been, and is daily bestowed upon them by thousands of amateur

naturalists, who cannot but be delighted with the wondrous variety of

form, and the beauteous colouring which these zoophytes possess.

 

A stranger could scarcely believe, on looking into an aquarium, that

the lovely object before him, seated motionless at the base of the

vessel, with tentacula expanded in all directions, was not a simple

daisy newly plucked from the mountain side, or it may be a blooming

marigold or _Anemone_ from some rich parterre--instead of being, in

reality, a living, moving, animal-flower.

 

One great advantage which the _Actiniæ_ possess over certain other

inhabitants of the sea-shore, at least to the eye of the naturalist, is

the facility with which specimens may be procured for observation and

study. Scarcely any rock-pool near low water mark but will be found to

encompass a certain number of these curious creatures, while some rocky

excavations of moderate size will at times contain as many as fifty.

Should the tide be far advanced, the young zoologist need not despair

of success, for, by carefully examining the under part of the boulders

totally uncovered by the sea, he will frequently find specimens of the

smooth anemone, contracted and hanging listlessly from the surface of

the stone, like masses of green, marone, or crimson jelly.