. The theory of evolution in the light of facts. se abdomen is exposed. a,eye ; b, antennae ; c, anus of crab ; d, shellopening; e, stalk; f, root of web, envelop-ing the intestines of the host, leavingthe germinal region free. {After Hertwig : Zoologie.) which remind one of free-living Swimming Crabs (twosuspended egg sacs), furthermore a series of transitionalforms between Swimming Crabs and these amorphousbeings, and above all their evolutionary history (em-bryogeny)—these were the factors which cleared uptheir systematic position. They pass through thetypical Cyclops stage of the Copepods,
. The theory of evolution in the light of facts. se abdomen is exposed. a,eye ; b, antennae ; c, anus of crab ; d, shellopening; e, stalk; f, root of web, envelop-ing the intestines of the host, leavingthe germinal region free. {After Hertwig : Zoologie.) which remind one of free-living Swimming Crabs (twosuspended egg sacs), furthermore a series of transitionalforms between Swimming Crabs and these amorphousbeings, and above all their evolutionary history (em-bryogeny)—these were the factors which cleared uptheir systematic position. They pass through thetypical Cyclops stage of the Copepods, and only when ^ R. Hartwig : Lehrbuch, p. 382. 208 THE THEORY OF EVOLUTION the females, and only the females, attach themselvesafter the pairing, do the retrogressive steps begin whichlead to the assumption of the almost limbless males remain much more crab-hke, they die afterthe pairing, their function being fulfilled ; the females,on the other hand, must now provide the eggs withnutrition, and therefore survive. Since they can do.
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