606 REPORT 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 larve of the 
marine fishes come into consideration. Some few teleosts (Scopelide, 
Trichiuride, et al.) occur sometimes in schools in the plankton and 
are partly autopelagic, partly bathypelagic. The remarkable Lepto- 
cephalide are possibly plauktonic larve (of Miurenoide), which never 
become sexually mature (7, p. 562), 
Fish eggs.—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 rdle 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). Butthe assumption from which he starts is wholly untenable. 
Hensen says (loc. cit.): 
It is 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 “in all 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 ave 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. g., crustacea and meduse. Many small medu- 
se, which belong to the most numerous animals of the pelagic fauna 
(e. g., Obelia and Lirope) produce relatively few eggs; as also copepods, 
the commonest 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 pelagic fish eggs 
not the slightest conclusion can be drawn as to the number of fish which 
develop from them and reach maturity. The major portion of the 
planktenie fish eggs and young are early consumed as food by other 
animals. 
