Volume II Part 12 (1/2)

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 s.h.i.+eld 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.)