The System of Nature Author:Edward Newman Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III. BIRDS A DISTINCT CLASS. It may be presumed, from the tenor of the preceding chapters, that I lay great stress on unity of design, and therefor... more »e I should not exempt any exterior division from the rules or principles applied in ascertaining the natural arrangement of the normal division. I must, however, admit that there appears to me sufficient ground for supposing the existence of some slight difference; for whereas the contents of normal groups are, by virtue of their central situation, strikingly heterogeneous, those of abnormal groups — such for instance as the marsupials and birds — are also, by virtue of their situation, much more homogeneous and accordant inter se; consequently their most abnormal forms scarcely recede so far from their respective centres as do those of the placental vertebrates : the birds, therefore, as a group, possibly form a more compact mass than the placentals; a suggestion which, if correct, will necessarily admit of a more extended application ; for winged insects appear to occupy a station, as regards the vertebrates, precisely analogous to that of birds, as regards the placentals. It seems scarcely possible to imagine a group of animals more uniform, more perfectly distinct, more decidedly marked, than birds. The separation of the marsupials from the placentals was a step that required much consideration, and when once decided on, it appeared necessary to defend it at considerable length, because, in their appearance, marsupials are essentially quadrupeds. With birds the case is altered : there is no child but can instantly distinguish between a bird and a quadruped, therefore the group is on all hands admitted as natural, and requires no argument in support of its distinctness. Were I to attempt to devise laws for nature ins...« less