2i8 EVOLUTION, GENETICS, AND EUGENICS 



worked in the mud and manure, making food for minute Infusorians 

 which multiply so rapidly that there may be a million from one in a 

 week's time. A cataract of Infusorians overflowed from box to pond, 

 and the water-fleas and other small fry gathered at the foot of the fall 

 and multiplied exceedingly. Thus the fishes were fed, and, as fish- 

 flesh is said to be good for the brain, we can trace a nexus from mud to 

 clear thinking. What was in the mud became part of the Infusorian, 

 which became part of the Crustacean, which became part of the fish, 

 which became part of the man. And it is thus that the world goes 

 round. 



Correlation between catches of mackerel and amount of spring 

 sunlight. — A curious and most interesting correlation has been 

 discovered by Dr. E. J. Allen between catches of mackerel and the 

 amount of sunlight. The more sunshine in May, the more mackerel 

 at Billingsgate. How does this work out ? Mr. G. E. Bullen shows 

 that "for the years 1903-1907 there appears to be a correlation 

 between the number of mackerel taken during May, and the amount 

 of Copepod plankton, upon which the mackerel feed, taken in the 

 neighborhood of the fishing grounds during the same month." 

 Mr. W. J. Dakin shows that the food of Copepods consists largely 

 of the vegetable organisms of the planlcton, such as diatoms, and of 

 Infusoria-like organisms called Peridinidae. But the production of 

 this microscopic plankton, the "stock" of the "seasoup," depends 

 partly on the composition of the sea-water, partly on the tempera- 

 ture, and partly on the amount of light available. There seems to be 

 no correlation between the surface temperature and the abundance 

 of mackerel, but Dr. Allen has shown a correspondence between 

 sunshine and the catches. Thus we see that, if all flesh is grass, 

 then in the same sense all fish is diatom. 



Nutritive chains in the deep sea. — If we pass from the sunUt 

 open sea to the floor of the deep sea — that strange, dark, cold, silent, 

 plantless world — ^we find carnivorous animal preying upon carnivorous 

 animal through long series — fish feeds on fish, fish on Crustacean, 

 Crustacean on worm, worm on still smaller fry, and all ultimately 

 depend on the basal food-supply — the ceaseless shower of moribund 

 atomies sinking from the surface waters many miles, it may be, over- 

 head, like the snowflakes on a quiet winter day. 



Dependence of one organism on another for the continuance of 

 the species. — Passing from "nutritive chains," we may select a few 

 illustrations of the dependence of one creature upon another for the 



