Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . s, which are carried on in so small a space:and this difficulty is much increased from thecircumstance that the organ in which they takeplace is itself only developed as the work pro-ceeds, its different parts being produced succes-sively in proportion as they are wanted, and theirform and structure undergoing frequent variationin the course of their developement. The most elaborate, and apparently accurateresearches on this intricate subject, are thoselately undertaken by M. Frederick Cuvi
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . s, which are carried on in so small a space:and this difficulty is much increased from thecircumstance that the organ in which they takeplace is itself only developed as the work pro-ceeds, its different parts being produced succes-sively in proportion as they are wanted, and theirform and structure undergoing frequent variationin the course of their developement. The most elaborate, and apparently accurateresearches on this intricate subject, are thoselately undertaken by M. Frederick Cuvier, fromwhose memoir* I have selected the followingabridged statement of the principal results of his * Memoires du Museum, xiii. 327 ; and Annales des SciencesNaturelles, ix. 113. FEATHERS OF BIRDS. 575 observations. It will be necessary in order toobtain a clear idea of the several steps of theprocess to be described, to advert to the structureof a feather in its finished state. For this pur-pose we need only examine a common feather,such as that represented in Fig. 228, where s is 228 229 230 231. the posterior surface of the solid stem, which, itwill be perceived, is divided into two parts by alongitudinal groove, and from either side of whichproceed a series of laminae, composing, with theirfibrils, what is termed the vane of the feather(v). The lines from which these laminae arise, 576 THE MECHANICAL FUNCTIONS. approach one another at the lower part of thestem, till they meet at a pomt, where the longi-tudinal groove terminates, and where there is asmall orifice (o), leading to the interior of thequill. From this part the transparent tubularportion of the quill (t) commences ; and at itslower extremity (l) there exists a second, or lowerorifice. The entire organ which forms the feather, andwhich may be termed its matrix, is representedin Fig. 229, when it has attained the cylindricform already described ; of which a is the apex,or conical part that rises above the cuticle
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