The doctrine of descent and Darwinism . es are separate; like ourselves during thefirst four or five days of hatching, they are withouta beak ; their extremities are tolerably like each other,as are ours for about the same time; not a single truefeather is to be found on their bodies, only thin feather-shafts, so that, even in the nest, we are more advancedthan they ever become; their bones are not very hard,and like ours, in our youth, contain no air at all; they 56 THE DOCTRINE OF DESCENT. are utterly destitute of air-sacs, and their lungs, likeours In early infancy, are not full-grown; a cr
The doctrine of descent and Darwinism . es are separate; like ourselves during thefirst four or five days of hatching, they are withouta beak ; their extremities are tolerably like each other,as are ours for about the same time; not a single truefeather is to be found on their bodies, only thin feather-shafts, so that, even in the nest, we are more advancedthan they ever become; their bones are not very hard,and like ours, in our youth, contain no air at all; they 56 THE DOCTRINE OF DESCENT. are utterly destitute of air-sacs, and their lungs, likeours In early infancy, are not full-grown; a crop- is com-pletely wanting; gullet and gizzard are, more or less,merged In a sac, all conditions very transitory in us,and, in most, the nails are awkwardly broad, as with usbefore breaking the shell ; the bats, which appear themost perfect, are alone able to fly; not the others. Andthese mammals which, so long after birth, are unable tofind their own food, and never rise from the ground,fancy themselves more highly organised than we ?. Fig. 7. Fig. 8. Nevertheless, there remains the fact of the parallelismof individual development with the systematic series towhich the Individual belongs ; and, among thousands ofexamples, we will select some of the most accessible andconvincing. Polypes have always been placed systemati-cally below the Medusae ; In the development of many SYSTEMATIC DEVELOPMENT. 57 MedusDS ( Fig. 3, p. 43), a polype-like condition isinterposed. The crinoid (Comatula), very common inthe Mediterranean, is in its mature condition freelymovable. This definitive development is, however, pre-ceded by a sessile stage (Fig. 7), during which thebody is attached to a stalk. During the larval periodthe animal resembles the permanently sessile genera,which, by all systematic rules, and by their geologicalposition, occupy a lower rank in the series of echino-derms. The crabs, or anourous Crustacea, are raised bysundry characteristics above their long-tailed congeners
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