606 REPORT OF COMMISSIONER OF FI^^H AND FISHERIES. 



provisionally limit ourselves to the vertebrates of the sea "carried 

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

 pelnjiic fishes) only the pelagic eggs, young brood, and larvte of the 

 marine fishes come into consideration. Some few teleosts {Scojyelidce 

 Trichiuridw, ct aJ.) occur sometimes in schools in the plankton and 

 are partly autopelagic, partly bathypelagic. The remarkable Lejyto- 

 cephaUchv are possibly planktonic larviie (of J\Inr(vnoid(v), which never 

 become sexually mature (7, p. 502). 



Fish cf/f/.s. — The planktonic 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 planktonic 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 i8 scarcely to be doubted that an opinion upon the relative wealth of various 



kinds of fish in the Baltic or in any other part of theocean whatever can be obtained 



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



Brandt also characterizes this proposition as very lucid and weighty 



(23, 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 

 hindrances to increase. He points out that "«? aU cases the average 

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

 indirectly on the number of seeds or eggs, but directly on the conditions 

 of existence under which they develop." Striking examples of these 

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

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

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

 many pelagic animals ; c. g., Crustacea and medusae. Many small medu- 

 sae, which belong to the most numerous animals of the pelagic fauna 

 {e. g., Obelia and Lirope) produce relatively few eggsj as also copepods, 

 the conmionest of all planktonic animals. Incomparably greater is the 

 number of eggs produced by a single large medusa or decapod, which 

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

 not the slif/htest eonelusion can be drawn as to the number of fish which 

 develop from them and reach maturity. The major portion of the 

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

 animals. 



