A treatise on zoology . Fio. XX. Si)ecialisatioii of ann-braiicliiiig. 1, a iiou-pimmlato, rcj^ularly dichotoinous arm () ;2, a less iTf^ular (licliotonious arm, a type comnioii in Cyathocriiioidea ; 3, 4, two staj^cs inthe, evolution of unilateral lieterotoniy ; 5, 6, 7, three stages in the evolution of bilaterallieterotoniy, culminating in i)innulation. For other types, see Fig. CX. right and left alternately. These smaller branches may themselvesundergo a similar process, and so form armlets {ramidi) borne main arm-branch (ramus). When theramules cease to branchthemselves,
A treatise on zoology . Fio. XX. Si)ecialisatioii of ann-braiicliiiig. 1, a iiou-pimmlato, rcj^ularly dichotoinous arm () ;2, a less iTf^ular (licliotonious arm, a type comnioii in Cyathocriiioidea ; 3, 4, two staj^cs inthe, evolution of unilateral lieterotoniy ; 5, 6, 7, three stages in the evolution of bilaterallieterotoniy, culminating in i)innulation. For other types, see Fig. CX. right and left alternately. These smaller branches may themselvesundergo a similar process, and so form armlets {ramidi) borne main arm-branch (ramus). When theramules cease to branchthemselves, and are reg-ularly placed on alter-nate sides of successivebrachials of the mainbranch, they are calledpinnulae, and the arm ispinnulate. This pro-cess of evolution hasbeen phylogeneticallytraced in Botryocrinus(Fig. XXL), while theprimitively dichotomousorigin of the pinnulesmay be seen in thedeveloping pinnule, as P. said, is anarm in miniature; itdiffers in nothing but i/.±.
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
