File:Image from page 163 of "The origin and evolution of life, on the theory of action, reaction and interaction of energy" (1917) (cropped).jpg

English: Identifier: originevolutiono00osbo

Title: The origin and evolution of life, on the theory of action, reaction and interaction of energy Year: 1917 (1910s) Authors: Osborn, Henry Fairfield, 1857-1935 Subjects: Evolution Life -- Origin Publisher: New York, C. Scribner's Sons Contributing Library: MBLWHOI Library Digitizing Sponsor: MBLWHOI Library

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Text Appearing Before Image: sil), Cambrian to Ordovician, contrasted with a living specimen of thewideh- differing Tcrchratiihi, which ranges from Devonian to recent times. time, so that sea forms with an antiquity estimated at twenty-five million years can be placed side by side with existing seaforms with very obvious similarities of function and structure,as in the series arranged for these lectures by Mr. Roy W.Miner, of the American Museum of Natural History (Figs. 21,22, 24-27). Except for the trilobites, the existence of Crustacea inCambrian times was unknown until the discovery of the prim- 124 THE ORIGIN AND EVOLUTION OF LIFE itive shrimp-like form, Burgessia hella (Fig. 22), a true crusta-cean, which may be compared with Apus lucasanus, a mem-ber of the most nearly allied recent group. We observe aclose correspondence in the shape of the chitinous shield (car-apace), in the arrangement of the leaf-like locomotor appen-dages at the base of the tail, and in the clear internal impres- MEROSTOMATA RUSTACEA

Text Appearing After Image: Fig. 22. Horseshoe Crab and Shrimp, Cambrian and Recent. Molaria spinifcra, a mid-Cambrian merostome (after Walcott), compared witli the recent horseshoe crab, Limiilus polyplicmus.Btirg<🇸🇸a bclla, a shrimp-like crustacean of the Middle Cambrian (after Walcott), compared with the very similar Apus lucasanus of recent times. sions in Burgessia of the so-called kidneys, with theirbranched tubules. The position of these organs in Apus isindicated by the two light areas on the carapace. Otherspecimens of Burgessia found by Walcott show that the taper-ing abdominal region and tail are jointed as in Apus. The age of the armored merostome arthropods is alsothrust back to mid-Cambrian times by the discovery of severalgenera of Aglaspidas, the t}qDical species of which, Molariaspinijera Walcott, may be compared with that living fossil, CAMBRIAN INVERTEBRATES 125 the horseshoe crab {Limulus polyphemns), its nearest modernrelative, which is beheved to be not so closely related to thephyllop

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