April 22, 1880] 



NATURE 



593 



over 1,000 fathoms orange and mango leaves, sugar-cane, 

 nutmegs, and land-shells in profusion, and many hermit- 

 crabs actually inhabiting tubes of bamboo instead of 

 shells. We found a land-crab once in 450 fathoms ; no 

 doubt it had drifted out hanging on to some floating 

 object, and had sunk to the bottom, being unable to swim. 



The numbers of animals to be found in the deep sea 

 decrease rapidly in proportion as the depth exceeds 2,000 

 fathom?, and very probably the greatest depths have very 

 little life in them. We at present know only of Rhizopods 

 as inhabiting them. Even in depths of less than 2,000 

 fathoms the shallower waters are most productive, and 

 probably the deep-sea fauna is most abundant not far 

 from the upper limit of its range. It is here, in from 200 

 to 400 fathoms, that such forms as Pentacrinus are most 

 numerous. Here in many places these animals, a few 

 years ago the greatest of rarities, cover the sea-bottom, 

 thickly set like trees in a forest, still as abundant a? ever 

 they were in geological times. It is probably scarcity in 

 supply of food which limits the quantities of animals in 

 great' depths. Xo doubt food is always most abundant 

 near the coasts. 



Some animal forms appear to be dwarfed by deep-sea 

 conditions of life. Others attain under them gigantic 

 proportions. It is especially certain Crustacea which 

 exhibit this latter peculiarity, but not all Crustacea, for 

 the crayfish-like forms in the deep sea, are of ordinary 

 size. I have already referred to a gigantic Pycnogonid 

 dredged by us. Mr. Agassiz dredged a gigantic Isopod 

 eleven inches in length. We dredged also a gigantic 

 Ostracod. The increase in size depends probably on 

 lack of enemies rather than on abundance of food. 



The unhappy deep-sea animals have not escaped their 

 parasites in their cold and gloomy retreat. The tube of 

 the Cerirmthus, of which I showed a figure, was full of 

 Nematode worms. Crinoids are beset by a Myzostomum, 

 and one deep-sea shrimp was found with a parasitic 

 Gordian worm coiled up inside its body, filling it almost 

 entirely. I have already described the vegetable parasites 

 of corals. 



The existence of colour in deep-sea animals is a very 

 interesting fact. Some of the animals, as for example 

 many of the fish, have lost their colour in the dark, and 

 have become simply black or white. Others are most 

 brightly coloured, having retained through countless 

 generations the colouring of their shallow-water ancestors. 

 Some, like the deep-sea shrimps, which are almost always 

 of an intensely bright red colour, seem to have developed 

 a special amount of colouring in the depths. The 

 phosphorescent light of deep-sea Alcyonarians, when 

 examined by the spectroscope, is seen to consist of red, 

 yellow, and green rays only. Hence only these colours 

 would be effective in the deep sea, and no blue animals 

 were dredged from any considerable depths. 



Colouring matters however need not always have a 

 decorative object in existence. Certain chemical com- 

 pounds formed within the bodies of animals for various 

 physiological purposes may happen to have a peculiar 

 action on light so as to be coloured, but this colour- 

 producing property may be a waste or bye-product, so 

 to speak, and only be turned to advantage by certain 

 animals as a subsequent improvement. The fact that 

 our own blood is red is probably an instance in point. 

 In most mammalia the blood is entirely in the dark 

 throughout the animal's life, and never acts on the light 

 so as to exhibit its colour, which is to these animals use- 

 less. In ourselves the colour has been turned to advan- 

 tage for decorative purposes. The colouring matters of 

 some deep-sea animals may thus be retained, because the 

 substances yielding the colours are necessary for the well- 

 being of the animals, and these substances happen to 

 be coloured, just as sulphate of copper is blue, though 

 chemists seldom employ it because of its colour. 



As an example of the vividness of deep-sea colouring 



matters, may be cited that of Pentacrinus. Here (Fig. 

 17) is a Pentacrinus dredged from 400 fathoms near the 

 Azores. The animal may be briefly described as a star- 

 fish turned upside down and set on a stalk. When 

 freshly dredged Pentacrini are put into spirit, their 

 colouring matter dissolves out and tinges the spirit of an 

 intense purple red. (The light was thrown upon the 

 screen through a solution of this colouring matter in 

 spirit, from specimens of Pentacrinus dredged in 650 

 fathoms.) The colour is a most beautiful red. It is red 

 when acid, but when a few drops of ammonia are added 

 to it, it turns to an intense green. Very probably this 

 colouring matter is as ancient as the genus Pentacrinus 

 itself. 



The colouring matter yields a well-defined absorption 

 spectrum. The acid solution (Fig. 18) shows two dark 

 bands in the yellow and a faint one in the green, and the 

 alkaline green fluid a dark one in the red, with two fainter 



HI 



Fig. 18.— Spectra of the acid and alkaline solutions of the' colouring matter 

 of Pentacrinus in spir.t The acid spectrum above and the alkaline 

 below. The fine lines are solar lines. 



ones in the yellow and green. By means of this double 

 set of lines this colouring matter can be almost certainly 

 identified, although its chemical composition has never 

 been investigated. 1 



A good many other colouring matters of deep-sea 

 animals give well-marked absorption spectra, and can be 

 similarly identified, and it is most interesting to find that 

 the very same colouring matters found in deep-sea ani- 

 mals occur also in allied shallow water and surface forms. 

 Thus numerous deep-sea corals and sea-anemonies are 

 tinged of a madder-red colour by the same pigment, 

 which is abundant in many jelly-fish which float on the 

 sea surface. The red colouring matter of the deep-sea 

 shrimps is also identical with that which occurs in smaller 

 quantities in nearly all the microscopic Crustacea with 

 which the sea surface is crowded. 



In conclusion I would merely impress upon you again 

 that the most important subject now remaining to be 

 investigated with regard to deep-sea life is the range of 

 life at the various depths between the surface and the 

 bottom of the ocean. 



A MAGNETO-ELECTRIC GYROSCOPE 



THIS is the name of an apparatus invented by M. W. 

 de Fonvielle, editor of Electricity, after having wit- 

 nessed an experiment by M. D. Lontin. This gyroscopic 

 machine was exhibited by M. de Fonvielle to the Royal 

 Society on the 15th inst., when a paper by him was read 

 by Prof. Stokes. The instrument can now be seen at 

 Elliot's, St. Martin's Lane. 



The object of the apparatus is to demonstrate new 

 properties of induction currents brought into play in a 

 magnetic field, and which give a continuous rotatory 

 motion to movable pieces of iron of various forms (Fig. 1). 

 The apparatus consists essentially of a galvanometric 

 frame of any shape. In the first model which has been 

 brought over to England the galvanometric frame is a 

 rectangular one, above which is placed a horseshoe- 

 magnet, supported by a vertical axis round which the 



' See H. N. Moseley. "On the Colouring Matters of Various Animals, 

 especially Deep-sea Forms " (Quart. Jourii. Micro. Sci., vol. xvii., new ser., 

 p. 0- 



