. The origin and evolution of life, on the theory of action, reaction and interaction of energy. D EVOLUTION OF LIFE Cambrian strata members of this order differentiated into at least three widely distinct famiUes. The worms, including swimming and burrowing annulates, are represented in the Bur-gess fauna by a very largenumber of specimens, com-prising nineteen species, dis-tributed through elevengenera and six of these are of theorder Polycha?ta, as, for ex-ample, Worthenella cambria,in which the head is armedwith tentacles, while thesegmented body and thecontinuous series of b
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. D EVOLUTION OF LIFE Cambrian strata members of this order differentiated into at least three widely distinct famiUes. The worms, including swimming and burrowing annulates, are represented in the Bur-gess fauna by a very largenumber of specimens, com-prising nineteen species, dis-tributed through elevengenera and six of these are of theorder Polycha?ta, as, for ex-ample, Worthenella cambria,in which the head is armedwith tentacles, while thesegmented body and thecontinuous series of bilobedparapodia are very compared with suchtypical living polychaetes asNereis virens and Arabellaop alma (Fig. 25), we haveclear proof of the modernrelationships of these mid-Cambrian species, as well asof Cambrian sea-shore andtidal conditions closelysimilar to those of the pres-ent time. A specializationtoward the spiny or scalyannulates at this period is emphasized in such forms as Canadia spinosa (Fig. 25), a slowly moving form which shows a development of lateral cha^tae and. Fig. 25. Worms (Annulata) of the IMiddleCambrian and Recent Seashores. Canadia spinosa, a mid-Cambrian form (afterWalcott) with overlappinj^ groups of scale-like dorsal spines, resembling those of the liv-ing AphroditidcE, such as Polynoe sqiiamata. Worthenella cambria, a worm of mid-Cambriantimes (after Walcott), compared with Nereisvirens and Arabella opalina, recent marineworms. CAMBRIAN INVERTEBRATES 129 CH/ETOGNATHA overlapping groups of scale-like dorsal spines comparable onlyto those of the living Aphroditidae. An example of this latterfamily is Polynoe sguamala, furnished with dorsal scales. Stillother recent forms, such as Palmyra aiirijera Savigny, havegroups of spinous scales closelyresembling those of Canadia. Even the modern freely pro-pelled Chcrtognatha have theirrepresentatives in the mid-Cambrian, for to no other groupof invertebrates can Amlskwiasagittiformis Walcott (Fig
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