606 REPOKT OF COMMISSIONER OF FISH AND FISHERIES. 



provisionally limit ourselves to the vertebrates of the sea "carried 

 involuntarily with the water," and as such (apart from a few small 

 pelagic fishes) only the pelagic eggs, young brood, and larva' of the 

 marine fishes come into consideration. Some few tcleosts {ScopcluUv, 

 TricliiuriflfVj ct al.) occur sometimes in schools in the ])lanktou and 

 are i)artly autopelagic, partly bathypelagic. The remarkable Lepto- 

 cephaUdw are i)<>ssibly planktonic lavvjc (of Mnrxvnoidcv), wiiich never 

 become sexually mature (7, p. 5()2). 



Fish cfips. — The ])lanktonic fish eggs, found in great numbers at the 

 surface of the sea, as well as the young fish escaped from them, play 

 without doubt a great role in the natural history of the sea. Hensen, 

 whose i)lanktonic investigation started from this point, had thereupon 

 "based the hope to obtain a far more definite conclusion upon the supply 

 of certain species of fishes than had hitherto seemed to be possible" (9, 

 p. 39). But the assumption from which he starts is wholly untenable. 

 Hensen says {loc. eit.): 



It is scarcely to be doubted that an opinion upon tlie relative wealth of various 

 kinds of fish in the Baltic or in any other part of theoccau^vhatevercan be obtained 

 through the determination of the rxuantity of eggs in the area under consideration. 



Brandt also characterizes this proposition as very lucid and weighty 

 (L>3, p. 517). 



This standard proposition of Hensen and Brandt, from which a series 

 of very important and complicated computations are to be made, was 

 disposed of in a brilliant manner thirty years ago by Charles Darwin. 

 In the third chapter of his epoch-making " Origin of Species," treating 

 of the "Struggle for Existence," Darwin, under the head of Malthus' 

 theory of population, speaks of the conditions and results of individual 

 increase, the geometric relation of their increase, and the nature of the 

 hiiulranccs to increase. He points out that ^Hn all cases the average 

 number of individuals of any species of plant or animal depends only 

 indire(;tly on the luimber of seeds or eggs, but directly on the conditions 

 of existence under wiiich they develo})." Striking examples of these 

 facts are everywhere at hand, and I myself have mentioned a number of 

 them in my "Natural History of Creation" (30, p. 143). Still, to draw 

 a few examples from the life of the plankton, I recall in this connection 

 many pelagic animals ', e. </., Crustacea and medusai. Many small medu- 

 sa*, which belong to the most nunu'rous animals of the i^elagic fauna 

 (e. {/., Obelia and Li rope) produce relatively few eggs; as also copepods, 

 the commonest of all jdanktonic animals. Incomparably greater is tlie 

 number of eggs ])roduced by a single large medusa or decapod, which 

 belongs to the rarer species. So, from tlie number of i)elagic fish eggs 

 not the slifjhtest conclusion can be draw n as to the number of fish which 

 develo]) fioni them and reach maturity. The nnijor portion of the 

 planktonic fish eggs and young are early consumed as food by other 

 animals. 



