Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals (1907) (14586682489)

Identifier: evolutionanimall00jord (find matches)
Title: Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals
Year: 1907 (1900s)
Authors: Jordan, David Starr, 1851-1931 Kellogg, Vernon L. (Vernon Lyman), 1867-1937
Subjects: Evolution
Publisher: New York, D. Appleton and Company
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library



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FIG. 213.—Trichina spiralis,the terrible parasite of pork:a, Male; b, cyst; c, female. PARASITISM AND DEGENERATION 357 velops in the upper intestine. It feeds on the blood of theyoung seal, which finally dies from anaemia. On the sandbeaches of the seal islands in Bering Sea there are every year
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thousands of dead seal pups which have been killed by thisparasite (Fig. 214). On the rocky rookeries, the young seals are not affected by this parasite.24 358 EVOLUTION AND ANIMAL LIFE Among the more highly organized animals the results of aparasitic life, in degree of structural degeneration, can be morereadily seen. A well-known parasite, belonging to the Crus-tacea—the class of shrimps, crabs, lobsters, and crayfishes—isSacculina. The young Sacculina (Fig. 215, A) is an active, free-swimming larva much like a young prawn or young crab. Butthe adult bears absolutely no resemblance to such a typicalcrustacean as a crayfish or crab. The Sacculina after a short B