TRANSACTIONS OF SECTION D. 749 



receded from. Unfortunately our knowledge of pelagic vegetable life is very im- 

 perfect, and it is to be hoped that botanists may be led to take up the subject and 

 bring together what is known with regard to the geological ranges and abundance 

 of the various larger seaweeds, trichodesmium, diatoms, and other algfe by which 

 the sea-surface is inhabited. It will, then, be possible to form a nearer estimate 

 of the extent to which these plants are capable of forming a sufficient ultimate 

 food-source for the greater part of the pelagic fauna, and through it of deep-sea 

 life. The question is of importance, because if the deep sea, having no ultimate 

 source of food in itself, derived its main supply from the coasts and land-surfaces 

 in the early history of the habitation of the globe by animals, there can have 

 existed scarcely any deep-sea fauna until the littoral and terrestrial faunas and 

 floras had become well established. 



Whether the littcral and terrestrial plants or the pelagic be proved to have 

 the larger share in composing the ultimate food-source of the deep sea, it seems 

 certain that the food as it reaches the deep sea is mostly in the form of dead 

 matter, and I imagine that the long but slender backwardly directed teeth of many 

 deep-sea fish, resembling those of snakes, are used rather as aids for swallowing 

 whole other fishes which have fallen from above dead, and thus making the best of 

 an occasional opportunity of a meal, than for catching and killing living prey. In 

 a lecture on ' Life in the Deep Sea,' delivered in 1880, 1 I suggested that putrefac- 

 tion of organic matter, such as ordinarily occurs elsewhere, may possibly be entirely 

 absent, in the deep sea, the bacteria and other microphytes which cause it bein°- 

 possibly absent. Some interesting experiments with regard to this question have 

 lately been made by M. A. Certes. 3 He added to sterilised solutions of hay- 

 extract, milk, broth, and other organic nutrient fluids mixed with sea-water, with 

 the usual necessary precautions, small quantities of deep-sea mud, or deep-sea 

 water, procured by the ' Travailleur ' and ' Talisman.' In some experiments air was 

 present ; others were made in vacuo. In nearly all the former putrefaction occurred 

 after some time, especially after application of warmth, and micro-organisms were 

 developed, whilst the latter remained without exception sterile, apparently indi- 

 cating that the microbes which five where air is absent are not present in the deep 

 sea. The others which developed in the presence of oxygen may possibly have 

 sunk from the surface to the bottom, and have retained their vitality, although it 

 is not improbable that they may be incapable of active existence and multiplication 

 under the physical conditions there existing. M. Certes is to make further 

 experiments on this question under conditions of pressure and temperature as 

 nearly resembling those of the deep sea as possible. In the deep sea the ordinary 

 cycle of chemical changes of matter produced by life is incomplete, there being no 

 plants to work up the decomposition products. These, therefore, in the absence of 

 any rapid change of the deep-sea waters, must accumulate there, and can only be 

 turned to account, when they reach the surface-waters on the littoral regions. 



Many interesting results may be expected to be obtained when the histology of 

 animals from great depths comes to be worked out, and especially that of the 

 special sense-organs. At present very little has, been attempted in this direction, 

 principally, no doubt, because deep-sea specimens are too precious to be used for 

 the purpose. In a remarkable scopelid fish dredged by the * Challenger ' from deep 

 water, Jpnops Murrayi of Dr. Gunther, the eyes are curiously flattened out and 

 occupy the whole upper surface of the mouth. They are devoid of any trace of 

 lens or iris, and, as appears from observations by Mr. John Murray and my own 

 examination of his preparations, the retina consists of a layer of long rods, with a 

 very thin layer indeed of nerve-fibres in front of it, and apparently no intervening 

 granular ganglionic or other layers. The rods are disposed in hexagonal bundles, 

 the free ends of which rest on corresponding well-defined hexagonal areas, into 

 which the choroid is divided. It is probable that aberrant structures may be found 



1 Lecture delivered at the Royal Institution, March 5, 1880, Nature, April 22. 

 p. 592. 



2 ' Sur la Culture, a, l'abri des Germes Atmospheriques, des Eaux et des Sediments 

 rapportes par les Expeditions du "Travailleur" et du "Talisman," 1882, 1883,' 

 Comptes-Rcndvs, No. 11, 11 mars 1884, p. 690. 



