Journals of Two Expeditions of Discovery in North-West and Western Australia Volume II Part 13

The animal here described belongs equally to the Indian and Atlantic Oceans, and appears, as far as my experience goes, never to venture to the south of 25 degrees south lat.i.tude. This is now the third species of animals which I have found to be common to the Atlantic and Indian Oceans, and which never venture beyond the warmer lat.i.tudes.

The question is how they got round the Cape of Good Hope, or Cape Horn?

Might we not hence infer that there was a time when the continent of Africa did not exist? and might not this argument be much extended? It could be combated by none of those causes which are advanced relative to the distribution of species on land; for,

1. The temperature of the water in southern lat.i.tudes is very cold at all seasons of the year.

2. These animals are extremely susceptible of all changes of temperature.

3. They have no means of warming themselves by exercise or motion.

4. The species of food which they subsist on is confined to the lat.i.tudes in which they themselves live.

5. They would have to traverse great distances in ungenial climes, and contend against adverse winds, the children of placid seas and genial suns hurried into giant waves and chilling storms.

6. It is not probable that they are swept along in currents, from the circ.u.mstance that in the one which flows along the coast to the eastward of the Cape we could find none of them, whilst upon its very edge they were in abundance.

Could however their eggs be swept along by a current, and after having been wave-tossed for months or years, be at last borne into waters sufficiently warm to hatch them, and the animals, finding themselves in a genial climate, have increased and multiplied?

The numerous little animals of the species which I have always considered to be the Velella of Lamarck went sailing merrily by us today; the least breath of wind made them turn round and round; and this was their mode of progression, the animal moved its little sail which I have before mentioned, and worked its tentaculae so vigorously as to make ripples in the water, in the midst of which it went buoyantly floating along.

Caught another fish (Stenopteryx Ill.u.s.tration 5) of the same species as that found on the 15th of July. The accompanying figure is drawn from minute measurements. The length of this specimen was 2.5 inches, its thickness through the thickest part 0.38.

What I had before imagined to be either a spine or fin turned out to be a pectoral fin.

It thus has two pectoral, one dorsal, and one ventral fin, properly speaking; but the greater part of the body is surrounded by some cartilaginous substance which it probably uses as a fin; under the line b c there is a curved portion of this matter, and above and attached to the fish is a line of round white silvery scales, about ten in number.

Between a and b there is another curved ma.s.s of transparent cartilaginous substance, along the bottom of which runs a spine to which is attached a fringe-like fin. There is a spine upon the back; the eye is very prominent and bright; upon the back, between the eye and the spine, there are successive stripes of purple and burnished gold, so that this little animal is one of the most gorgeously coloured denizens of the ocean. It swims about amongst the purple barnacles and pink nautili, seeking on the sh.o.r.es of these s.h.i.+ning islands its prey, the curious formation of its mouth being admirably adapted to enable it, whilst swimming under these painted floating islands, to crop off what it lists.

There were scarcely any gelatinous animals in the sea this day; but many Janthina sh.e.l.ls and Velella were round the s.h.i.+p, to which were attached barnacles of different species; amongst this group of islands numerous crabs were swimming about and running over them. Animals resembling a wood-louse were also in the sea, swimming and running about the floating sh.e.l.ls and barnacles.

We caught also a new species of Janthina, the float of which, instead of being nearly round and extending over the sh.e.l.l on each side, was spread like a spiral fold from the sh.e.l.l; the breadth of this fold was 0.45 inch, close to the mouth of the sh.e.l.l, and it gradually tapered off to a point, its length being 3.6 inches. This float being curved round like the tail of an animal, the whole thing bore the appearance of being a sort of snake, of which the sh.e.l.l was the head; the sailors called them caterpillars before I had examined them. The float was composed of two parts, one of which was only froth and the other was apparently some extraneous substance attached to the froth. The sh.e.l.l is very different from those of the other nautili in being much more deeply indented with circular striae.

July 18. South lat.i.tude 19 degrees 49 minutes; west longitude 3 degrees 10 minutes 15 seconds.

We have lately caught several specimens of Creseis. Each consists of a cylindrical tube, increasing in size from its broadest extremity to the centre where it is thickest, and decreasing from the centre to its other extremity, where it becomes a fine point. It is throughout its extent gelatinous, transparent, and of strong consistency.

There is apparently a valve at its broadest extremity.

Length 1.1 inch.

Breadth in centre 0.1 inch.

Breadth at mouth of wide extremity 0.08 inch.

We have several times caught a triangular, transparent, gelatinous animal; it is 0.18 inch in thickness, and in the outer pulpy gelatinous ma.s.s there is an interior sac, and strong muscular bands are marked across this. The sac is composed of three lobes, two of which have apparently no external opening, whilst at the end of the main lobe there is one which closes with a valve; through this I have seen them take in little animals, which reached no farther than the centre, from which the lobes radiate, when the sac became violently agitated, and made strong efforts to expel the foreign substance. This animal was very sensitive, more particularly about the opening of the entrance.

We caught today the lower part of the species of Diphyes which we had found on the 13th November 1837, in 30 degrees 7 minutes south lat.i.tude, in the Indian Ocean. This animal is thus distributed over a wide range.

We also found a very minute species of the animal similar to one which we caught on July 1st 1840. Those we caught today were scarcely 0.05 inches in diameter. They unfolded little wings and flew with them in precisely the way those did which I described on that day.

Nothing I have seen is more remarkable than the flight of these little animals; their wings are milk white and very large for their body, and as they fly, the ends, from their pliancy, bend over, which imparts to the motion a very graceful appearance; these wings are composed of a very fine membrane like that forming the wings of a bat. At one time these little animals hovered over a single spot like a bird of prey in the air, flapping their wings in just the same manner. At another time they darted forward with great rapidity, and the vibration of their wings was so rapid that I could not count them. When folded up they look like very minute gelatinous animals with a black internal spot, but when touched their sh.e.l.l can be felt. We saw a shoal of whales today.

We have caught lately a great many small animals, of which the following is the description; they swim about from one floating substance to another and are eaten by the little crabs which are numerous in these seas.

Length of body 0.18 inch.

Length of anterior part of body 0.1 inch.

Length of posterior part of body 0.08 inch.

Length of tail 0.08 inch.

Breadth across back 0.05 inch.

Depth from back to bottom of breast 0.06 inch.

Head and eyes, deep brilliant prussian blue; body brilliant prussian blue with a bluish green stripe on each side; tail white. Seen through a microscope these animals appear to be a beautiful dark burnished blue mottled with silver. The head is remarkably round and regular.

The body is divided into two portions. The anterior portion is made up of six rings or s.h.i.+elds, which lap over one another, and it is furnished with three legs on each side which terminate in a hooked claw; the posterior part is covered by three s.h.i.+elds, and there was only one leg on each side. I could not make out any tentaculae or antennae.

I was much struck by a curious circ.u.mstance today. As we caught a great many gelatinous animals I thought this a good opportunity of taking their temperature, which, after an observation so carefully made that no error could occur, was found to be 66 degrees 5 Fahrenheit, the temperature of the air at the same time being 74 degrees. The temperature of the water was now taken and was found to be 2 degrees 5 minutes more than that of the animals; thus giving these animals a temperature lower than that of the fluid in which they were immersed. I conceived that some error must have been made in the temperature of the water, it was therefore taken again and found to be 69 degrees as before; this appeared to me so remarkable that I drew up a table of all the experiments which had been made on this subject, the result of which is that the mean temperature of these kinds of animals appears to be 64 degrees 9 minutes Fahrenheit; and that the greatest variation in excess is 1 degree 7 minutes; and in defect 2 degrees 9 minutes Fahrenheit. Is it possible, then, that an animal can live in a fluid, the temperature of which is constantly varying, and preserve nearly a mean heat?

In the following tables I have entered every experiment but one which was made on the 17th of June, and in which I believe the animals to have been kept too long out of water.

(Experiments to determine the temperature of gelatinous animals which inhabit the sea:

Experiments to determine the temperature of sh.e.l.lfish inhabiting the open ocean:)

This last experiment was made from a sickly specimen which had been kept for some time in the water: the temperature of water above given is for that in which this animal was kept.

We caught again today many animals of the same family (Glaucus) as those of which a description is given in the journal for the 17th of June.

Also many shrimp-like animals (Alima) the bodies of which were divided distinctly into an interior and posterior portion; all the shrimp-like animals which we have caught whose bodies are thus divided swim by doubling up the posterior part close to the anterior, and then giving a stroke with great rapidity outwards. These little animals are very susceptible, and when they have been in the least injured their limbs remain in so constant a state of tremor that the motion communicated by them resembles that which would be caused by the pa.s.sage of a rapid succession of electric shocks, rather than any other I am acquainted with.

GEOLOGICAL OBSERVATIONS AT ST. HELENA.

July 21.

After visiting Longwood and Napoleon's tomb we rode to Flagstaff Hill to search for fossil sh.e.l.ls. The whole soil that I saw was composed of decomposed old volcanic rocks; but I saw no rock but basalt in different stages of decomposition; sometimes it a.s.sumed the form of porphyry. I also saw veins of quartz, gypsum, and jasper. On a part of Flagstaff Hill there was a thin stratum of calcareous earth, in which sh.e.l.ls are found.

My hip was so painful that I could not climb to the point where these were, but an artillery soldier ascended and brought down some, and of these I had several specimens given me; they are found a.s.sociated with bones which are apparently those of birds. None of these bones were given to me but I saw and examined several specimens. The sh.e.l.ls are very numerous at this point.

On returning into town I found several specimens of dead land sh.e.l.ls, apparently recent; these lay on the sides of the hills, partly buried in the soil, and bore the appearance of having been washed into this position by the heavy rains.

July 22.

Rode over in the morning to Longwood, and then proceeded to Gregory's Valley, lying between Longwood and The Barn. This valley, nearly 1700 feet in depth, appears at one period to have been the scene of great volcanic disturbances. The lowest rock I saw was a compact porphyritic one. The upper strata of basalt were in a state of rapid decomposition; but the whole of the valley was traversed by basaltic d.y.k.es in every direction; these crossed one another in such a way that it was easy to tell their relative ages; for instance several of them were in the form of:

So that one had been forced from its position by another long subsequently to its formation.

The general form of Gregory's Valley is a large basin bounded by a lofty precipitous mountain on one side called The Barn, and having a very narrow opening seaward, through which a small stream has cut its way. A remarkable circ.u.mstance connected with the basaltic d.y.k.es is that they are composed of a more compact basaltic rock than the basalt which they penetrate, so that whilst the rock has mouldered away these basaltic d.y.k.es have remained standing; and, as in the progress of their decay they split up, they present the appearances of walls built by human hands, with regular layers of stones, and which traverse the ravines of the island in all directions.

As might be expected, I found regular basaltic crystals in this valley, and also a variety of quartz ore, and other crystals, in the veins traversing the basalt. I also found the following remarkable section:

This was in a side valley or ravine leading from Gregory's Valley in a southerly direction.