544 



NATURE 



[Aprils, 1880 



shown quietly smoking his pipe whilst his dredge tows 

 astern catching bivalves (either a Cardium or a Pecten). 

 For the sake of clearness the artist has represented the 

 dredge as partly raised out of the water. On the margin 

 is the description, which my friend, Mr. F. V. Uickins, 

 has translated for me. The dredge is described as a 

 basket net which is dragged from the stern of a boat 

 scratching up sand and mud and the shell fish. The 

 particular shell fish here being caught are explained to 

 have been formerly considered poisonous, and it is said 

 that they are even now not considered very good, and are 

 never used in gentlemen's kitchens. 



f A great step in advance was made on board the 

 Challenger in the introduction by Sir George Nares of 

 the trawl-net as a substitute for the dredge in deep-sea 

 investigation. Still both the sounding and trawling 

 apparatus used on board the ship were very imperfect in 

 comparison with the apparatus now employed. Mr. 

 Alexander Agassiz, following Sir William Thomson's 

 improvements in methods of sounding, has introduced the 

 use of wire rope for trawling with, instead of the hempen 

 rope which we used. The wire rope has most important 

 advantages. It occupies only one-ninth of the space of 

 the hempen rope on board the ship, being only one inch 

 and a sixteenth in circumference. It is of galvanised 

 steel wire with a hemp core. It is not as big as my little 

 finger, and contrasts favourably with the large trawi ropes 

 of the Challenger. The wire rope is heavy in the water, 

 and need not be weighted when in use like the old rope. 

 Moreover it can be let run out and be wound in at such a 

 rate that three or four hauls can be got in one day in depths 

 over which the Challenger consumed a whole weary day for 

 one haul. 1 Mr. Agassiz has also improved the trawl-net. 

 Our trawl was an ordinary beam trawl which might fall on 

 its back on the bottom and be towed along in vain. This 



Fig. 2. — Mr. A. Agassii's deep 



one is, as will be seen from Fig. 2,- reversible. It has 

 two beams instead of one, as in the old pattern, and these 

 are fixed to the irons midway between the two margins 

 of the mouth of the net, one of which will scrape the 

 bottom on whichever side the trawl may fall. Mr. Agassiz 

 has also used with great success a simple iron bar with 

 twelve or fifteen swabs fastened on to it, and towed in a 

 transverse position. With this machine he brought up on 

 one occasion no less than 124 specimens of two large 

 species of Pentacrinus at one haul. 3 



I pass now to the consideration of life in the deep sea. 



As Prof. Weismann of Freyburg well said in a lecture 

 on the animal life of Lake Constance, 4 "The sea is the 

 birthplace of all animal and plant life ; from it animals 

 and plants have spread themselves on the land and into 

 the freshwaters which permeate it.'' This birthplace of 

 the various forms of life lay, no doubt, in shallow water 

 on the coasts, and thence has taken place the colonisation 

 of the deep sea on the one hand and of the land on the 

 other. 



It is only animals, however, which havejmade their way 

 into deep water. The absence of sunlight at great depths 

 is entirely prohibitive of the existence there of plants. 

 As far as I observed, we did not dredge any sea-weed in 

 the Challenger Expedition from a greater depth than 33 

 fathoms. Edward Forbes, however, found ordinary sea- 

 weeds in the .rEgean Sea down to a depth of 79 fathoms, 



1 A. Agassii: "Dredging Operations of the U.S. Coast-Survey Steamer 

 Blake," Bull. AIus. Coinp. Zool. vol. v. No. x, p. 7. 



■ Ibid., vol. v. No. 6. 3 //,;,/., vo l. v No. , 4l p. 296. 



4 Aug. Weismann, " Das Thierleben im Bodensee," s. 5. (Lindau : 

 Stettner, 1877.) 



5 Brit. Ass. Report, 1844, p. 165. 



though they were very scarce at that depth, and may 

 possibly not have grown there,- and Dr. Carpenter 

 dredged Corallinacea; in abundance in 150 fathoms in 

 the Mediterranean. 1 The question of the exact limit 

 of the different species cf sea-weeds in depth, and of the 

 absolute limit of plant-life altogether in the sea, is one 

 of great importance, and which has received but little 

 attention. It could easily be worked out by any yachts- 

 man on our coasts. 



In considerable depths only one plant is known to exist. 

 It is a lowly-organised parasitic fungus, which infests 

 corals, boring finely-ramified canals in their hard sub- 

 stance. This plant was found by Prof. Martin Duncan 1 

 in corals dredged from over 1,000 fathoms. Fig. 3 



Fig. 3. — Achlya fienetratu, Duncan. 



gives a view of its appearance taken from Prof. Duncan's 

 illustrations ; you would hardly recognise it as a plant. 

 It consists simply of a ramified mycelium and small spores. 

 Like some other fungi which live in mines and cellars, 

 it is able to live in the dark, because it nourishes itself 

 upon the tissues of its hosts. It belongs to the same 

 genus as a fungus that attacks the salmon in our rivers 

 and kills them, and is hardly to be distinguished from 

 that plant. It is an extremely ancient form, and infested 

 corals even in Silurian tiniest 

 Though plant life is so meagre, animal life is abundant 



Fig. i.-ActteUt abyssicola (Moseley). Attached to the stem of an Isis. 

 Fie. 5 .—£<lwardsia coriacea (Moseley). 



in the deep sea. There are hardly any of the groups of 

 invertebrate animals which inhabit our shores which are 

 not represented in deep waters. The only ones which I 

 know of as absent, as far as yet observed, from depths of 

 say 1,000 fathoms and more, are Planarian worms, and 

 certain minute animals such as Rotifers, Tardigrades, and 

 Infusoria. It is quite possible that these minute forms 



' Prec. R. S,,., 1872, P. 587- = **» *■ Soe - lE7<5 ' r - '**■ 



3 Quart , p. 205. 



