1869.] 



on the Scientific Exploration of the Deep Sea. 



477 



of the Inorganic world, under the influence of Light, is the special attribute 

 of Vegetation — is a doctrine so generally accepted, that to call it in ques- 

 tion would be esteemed a Physiological heresy. There is no difficulty in 

 accounting for the alimentation of the higher Animal types, with such an 

 unlimited supply of food as is afforded by the Globigerince and the Sponges 

 in the midst of which they live, and on which many of them are known to 

 feed. Given the Protozoa, everything else is explicable. But the ques- 

 tion returns, — On what do these Protozoa live ? 



127. The hypothesis has been advanced that the food of the abyssal 

 Protozoa is derived from Diatoms and other forms of minute Plants, which, 

 ordinarily living at or near the surface, may, by subsiding to the depths, 

 carry down to the animals of the sea-bed the supplies they require. Our 

 examination of the surface-waters, however, has afforded no evidence of the 

 existence of such Microphytic vegetation in quantity at all sufficient to 

 supply the vast demand ; and the most careful search in the Globigerina- 

 mud has failed to bring to light more than a very small number of speci- 

 mens of these Siliceous envelopes of Diatoms, which would most assuredly 

 have revealed themselves in abundance had these Protophytes served as a 

 principal component of the food of the Protozoa that have their dwelling- 

 place on the sea-bed. — Another hypothesis has been suggested, that these 

 Protozoa, which are so near the border of the Vegetable kingdom, may be 

 able, like Plants, to generate Organic Compounds for themselves, — manufac- 

 turing their own food, so to speak, from Inorganic materials. But it is 

 scarcely conceivable that they could do this without the agency of Light ; 

 and, as it is obviously the want of that agency which excludes the possibi- 

 lity of Vegetation in the abysses of the ocean, the same deficiency would 

 prevent Animals from carrying on the like process. 



128. A possible solution of this difficulty, first offered by Professor Wyville 

 Thomson in a Lecture delivered in the spring of 1869, has received so remark- 

 able a confirmation from the researches made in the ' Porcupine ' expedi- 

 tion, that it may now be put forth with considerable confidence. It is, he re- 

 marked, the distinctive character of the Protozoa, that " they have no 

 special organs of nutrition, but that they absorb water through the whole 

 surface of their jelly-like bodies. Most of these animals secrete exquisitely 

 formed skeletons, sometimes of Lime, sometimes of Silica. There is no 

 doubt that they extract both of these substances from the Sea-water, 

 although Silica often exists there in quantity so small as to elude detec- 

 tion by chemical tests. All Sea-water contains a certain amount of Organic 

 matter in solution. Its sources are obvious. All rivers contain a large 

 quantity ; every shore is surrounded by a fringe, which averages about a 

 mile in width, of olive and red Seaweeds ; in the middle of the Atlantic 

 there is a marine meadow, the Sargasso Sea, extending over 3,000,000 

 of square miles ; the sea is full of Animals which are constantly dying and 

 decaying ; and the water of the Gulf-stream especially courses round coasts 

 where the supply of organic matter is enormous. It is, therefore, quite 



VOL. XVIII. 2 o 



