Total length of blue base 1.7 inches.

Breadth of blue base 1.0 inches.

Height of centre of crest 0.5 inches.

Rim round crest, in breadth 0.55 inches.

This animal differed from those caught on the 11th November 1837, in the following particulars: It was much larger. The base of the animal consisted of two parts. The centre portion was an elliptically-formed cartilage, elevated in the centre, and marked with eighteen concentric striae, which became thinner and thinner as they approached the centre.

No striae were visible on the elevated crest with which the animal swims, but this crest was furnished or fringed with a thin moveable flap, 0.55 inches in breadth, which ran quite round it. The animal has the power of flapping this to and fro constantly, as a fish does its tail.

The outer portion of the base was of a pale prussian blue colour, increasing in depth of shade both to the outer and inner edges. Many minute black spots were dotted all over this. The underside of the outer base was of a very dark prussian blue colour, and its lower interior edge was furnished with rows of blue tentaculae, which the animal uses as an elephant does its trunk. The whole interior surface of the oval cartilage is furnished with successive rows of white tentaculae, and in the centre is a long thin white tube, apparently its mouth.

These animals always swim in company. You see a number together, varying from four or five to twenty or thirty; these are all within a few feet of one another, and you may then pa.s.s over several miles and not see any more.

They produce countless numbers of little eggs, of a pale brown colour; these are apparently deposited from the interior white tentaculae, and cannot be estimated they are so numerous.

We also caught a minute fish, 0.6 inches in length; a minute species of nautilus, blue, marked with striae, or grooved, and thus different from what we caught on the 15th; a shrimp-like species of animal 0.5 inches in length; the lower part of a species of Diphyes, which had been caught on the 12th and 13th of November 1837; some minute animals, appearing to be the young of the larger species of Velella which we had taken; they were, like this animal, at first blue, but turned red soon after being put into spirits; also a very minute pale blue species of nautilus, I think the young of the kind we caught on the 15th July.

Caught a number of gelatinous animals, differing however apparently in species from any we had found before. Some were of the family of crystal-shaped animals with blue spots, so often mentioned in this journal; also several animals of the family figured June 17th, but which differed from them in the colour of their spots. We caught today a Portuguese man of war (Physalis) of a very different species from those which we had taken in the Indian ocean. This one had a much larger sac, or float, than the others, and the float was furnished with a crest.

July 15. South lat.i.tude 20 degrees 20 minutes; west longitude 2 degrees 17 minutes.

The same animals mentioned in the last paragraph of July 14th were again caught this day. A great number of the Velella were also taken.

Caught a small fish:

Length 1.2 inches.

Breadth over roundest part 0.48 inches.

For a particular description, and figure of a finer specimen, see below.

The mouth and eyes of this fish were placed in a curious manner. Its food appeared to be the same as that of the other fish taken this day.

Caught two curious little crabs (Nautilograpsus) one pale blue, and the other of a pale pink colour: also, another little pale blue crab:

Length of antennae 0.15 inches.

Length of body 0.34 inches.

Breadth of ditto 0.12 inches.

Caught a small animal shaped like a wood-louse (Cymothoa) having nine rings apparent on the back, and I think seven legs on each side, also, a tail-like fin on each side, which, when closed under its belly, formed a sort of shield for the lower part of the abdomen. Antennae, transparent with pale brown tips, and a few pale brown spots in them, colour pale blue down centre of the back, dark prussian blue on each side. It had the power of rolling itself up nearly double; in the same manner as a wood-louse, but not quite so close; eyes distinct and prominent. It lived a long time out of water, and appeared to me exactly like an animal I caught on the 21st November 1837, in south lat.i.tude 24 degrees 19 minutes; east longitude 107 degrees 8 minutes.

We also this day caught a Janthina. They have a little valve for the purpose of taking in air, with which to expand their float. These animals go in company. They emit when touched a brilliant scarlet dye. A similar animal caught on the 20th November 1837, in south lat.i.tude 25 degrees 12 minutes; east longitude 106 degrees 49 minutes, emitted a violet-coloured dye. The emission of this evidently depends upon their being irritated, as I found by many experiments.

The method in which this animal fills its float is curious, it throws it back, and gradually lifts the lip of the valve out of water, until the valve stands vertical, it then closes the valve tightly round a globule of air, around which it folds, by means of the most complex and delicate machinery. The valve is then bent over until it touches the edge of the float nearest the head, and when it is in this position, the portion of it which is inflated with air looks like a bladder, the air gradually is expelled into the float, and as this process takes place the bladder in the valve diminishes, and the valve becomes by degrees like a lip pushed forwards until it lies flat on the float. The valve is composed of two portions, a cup and a lip. The time occupied from first removing the valve from the float, until the inflation, and the expulsion of air into the float being completed, so that the valve begins to move again, is 61 seconds, from the mean of several experiments.

These animals have also the power of compressing the valve into a hollow tube, which they elevate above the water like a funnel, and draw down air through it.

The colouring matter which they emit has no stinging, electric or deleterious properties whatever, that I could discover. I found that when this colouring matter was mixed with water, it became of a deep blue. In those which I caught in November 1837, I may have been deceived, and the colouring matter might also possibly have been scarlet directly it was emitted. It is difficult to conceive what use this liquid can be to the fish against its foes, yet it certainly uses it as a means of defence.

To one of these sh.e.l.ls, the fish in which was alive and well, we found attached a number of barnacles, some of which were of large size.

This sort of Janthina was very abundant; today we caught eight, and saw great numbers of them: yesterday we caught a smaller one of a different species. (Janthina exigua.)

This kind of Janthina is attached to its float by a sort of peduncle, which it has the power of elongating, so that the fish itself sinks, with its sh.e.l.l, and yet remains attached to the float, which continues at the surface. In one instance, I saw this peduncle elongated to a length of 0.9 inches. It may, of course, have the power of sinking itself much lower than I have seen it do. When it is in this state, the apparatus with which it fills the float remains behind the peduncle in a state of perfect quiescence.

The scarlet fluid emitted by this animal is of such a consistency that it can be drawn away from it out of the water, like a glutinous thread.

A part of the animal requires attention, it is composed of an outer cup, or circular lip, which it has the power of contracting or expanding in the same manner as the valve; and when opened out like a cup, an orifice can be seen at the bottom of it. It can also expand, and make broad the arm; and it then appears to use them as sails.

This species of Janthina, I afterwards found, has the power of in some manner taking in by suction a quant.i.ty of water, which it can suddenly expel again with great violence, sending it out as if from a squirt.

We caught, also, an extraordinary fish this day. Its mouth has the appearance of being situated on its back; a fin, 0.4 inches in length, projected directly out from one side of the fish, and there was every appearance of a perfectly similar one having been torn from the other side; a hard h.o.r.n.y membrane projected from underneath the stomach of the animal, being apparently a sort of fin.

Its colour was of a silvery metallic l.u.s.tre, having in parts a burnished appearance, except where it is shaded (see Ill.u.s.tration 5 and below) and then it was of a dark green colour; the tail was perfectly transparent, except just where it joined the body, and there, where the shaded line is, it was dark green.

This fish was swimming about, apparently preying on the tentaculae of the barnacles, of which there were numbers round the ship attached to the dead Velella, some of which I had caught yesterday; it appears therefore probable that its mouth was placed in so extraordinary a position to enable it to seize this pendant prey.

We caught this day a number of Velella, which are furnished with crests; some of them were dead, and nearly always when such was the case we found a species of barnacle attached in great numbers to them. When these animals had only recently died, so that the whole of their blue base had not been detached from them, the barnacles were generally very minute, so that the naked eye could only just detect them, and there were no large barnacles on the same fish: now, how did the minute ones get there? As the barnacles grew larger, the remains of the velella changed into large excrescences, half the size of a walnut.

We caught also several little animals, all of the same species, which swam about on the surface of the water with the greatest rapidity, performing the same kind of evolutions that we see in a little black and white insect (Gyrinus) which swims on the top of tranquil pools in England.

July 16.

This day a curious animal was caught, perfectly diaphanous; total length 0.8 inch; length of third leg, 0.4 inch; this was provided with a claw like a crab; head shaped like a gra.s.shopper, 0.2 inch in length, and placed like the head of a gra.s.shopper, at right angles to the body; eyes black and prominent, apparently four, two on each side; first and second legs of nearly the same length; the third leg nearly double the length of either of the others; five on each side. The top of the head is divided into two prominent k.n.o.bs, one on each side, which, viewed through a microscope, appear to be minutely reticulated.

The animal may be considered as consisting of four portions: the head; the upper part of the body, 0.18 inch in length, and divided into five rings; the lower part, consisting of one shield-like portion, 0.12 inch in length, the body at the lower portions of this decreases almost to the thickness of a thread; the tail, 0.3 inch in length, and divided into three shield-like pieces, laid one over the other as in the shrimp (imbricated); at the lower extremity of each of these scales there is on each side a fin-like leg, in addition to those above-mentioned. Breadth of the animal across its head, 0.2 inch, and this was the broadest part of it. It lived for some time out of water, and even when put into spirits, it swam in an extraordinary manner, falling head over heels every time, which motion it accomplished by swimming on its back and making rapid strokes with the fin-like legs with which it is provided behind.

We also caught today several little crabs and barnacles. I kept one specimen, to show old and young barnacles attached to the same Velella.

The sea was, this morning, covered in places with fleets of the Velella of Lamarck; also with great numbers of the species of Janthina which I described yesterday; to both of these kinds of animals large cl.u.s.ters of barnacles were frequently attached. These barnacles preyed on the different gelatinous animals which were swimming about. It was curious to see them seize on these with their hooked tentaculae and draw them in, whilst the acalepha, or gelatinous animal, contracted and dilated itself with all its might and main, endeavouring to escape. We saw two or three times very large shoals of porpoises ahead of us, and when we reached the spot where they had been we found the sea quite cleared of the animals with which it was covered in other places, so that we imagined the porpoises must have been feeding on them. We saw also a whale and a shark today.

Although these little floating animals were so numerous there were but very few of the gelatinous species to be seen, and they were chiefly of the larger sorts. I saw one of the species (Glaucus) of which I have given a sketch, on the 17th of June. Like all the animals of this species which we caught to the westward of the Cape it had a red intestinal spot in it; but excepting in its great size it differed in no respect from the others which I had seen: this one was at least a foot in length.

A number of black minute animals were caught, which, at a rapid glance, looked not unlike fleas with long feelers or antennae.

We caught also this day an animal (Salpa) which consisted of a gelatinous transparent bag, having an orifice provided with a valve that opened and closed the orifice at pleasure; there was no other opening to the sac that I could discover; I pa.s.sed the end of a pencil down it, but although it pa.s.sed readily through the valve it could not at first pa.s.s through the bottom of the gelatinous sac; but I afterwards found that this was an error, and that the pencil could be pa.s.sed right through the body of the animal, which was provided with a valve at each end. I found also that the united animals had the power of swimming with either end foremost.

There was an intestinal tube in the animal of a dark reddish brown colour. This animal appeared to exist very badly alone, fourteen of them were always found united together by a plane; they then formed a ma.s.s shaped like half an orange and having a cup at its upper surface; the intestinal ca.n.a.ls, when they are in this position, are all brought near to one another, and the whole ma.s.s looks not unlike a flower; they are united to one another by so thick a fluid that it is very difficult to separate them. If one or more are torn away from the ma.s.s the outside ones immediately join together and form a united ma.s.s again, of the original shape. They open the orifices at different times: that is, two or three open theirs at the moment that some of the others are closing, so that no regular or simultaneous movement takes place between the different animals. This irregular movement of the animals gives to the whole body an irregular rotatory motion; but when one is separated from the others it can only drive itself round and round upon its own centre, and has not the faculty of propelling itself as the other acalepha have.

They also swim with either end foremost, in the manner the other acalepha do.

We saw also some animals of this cla.s.s, and nearly as large as the ones I have just described, but they differed in their form and mode of attachment, and joined themselves in long strings, two deep, so as to look like gelatinous snakes. I have before described animals of this cla.s.s with blue spots. I think that a good mode of cla.s.sifying these animals would be from their form of arrangement when united.

July 17. South lat.i.tude 19 degrees 47 minutes; west longitude 3 degrees 5 minutes 30 seconds.

Found a small animal (Cymothoa) like a wood-louse, similar to the one we caught on the 15th of this month and to another taken on the 21st of November 1837. It had seven legs on each side, besides the five which when taken out of the water it folded over its abdomen; the colour the same as before described.

Length 0.52 inch.

Width over broadest part 0.2 inch.

Length of antennae 0.2 inch.

Ill.u.s.tration 4, exactly the size of life, gives a good idea of it. It lived out of the water for two or three hours and did not die until put into spirits; it ran about on the table as well as it swam in the water, so that it was evidently amphibious. It swam about from a dead sh.e.l.l of the Velella, to a nautilus, and from that again to some barnacles; each sh.e.l.l that it reached it climbed up, and folding up its fins ran all over it, so that it appeared like a little navigator which was roving from island to island in the ocean, seeking food and nourishment from all of them. Are not the ways of nature very wonderful? This little animal was at least 500 miles from any land, as we term it, yet it was surrounded by sunny islands, teeming for it with the most delicious food, and where it either basked in the warm daylight, or shaded itself in some oozy recess, as seemed most pleasant to it.

When walking on these substances it used its antennae exactly as insects do, and showed an extraordinary degree of susceptibility when touched. I do not know that I have ever seen an animal which more decidedly evinced an acute sense of feeling and dread of pain.