Huxley’s work upon birds, like his work in many other branches of anatomy, has been so overlaid by the investigations of subsequent zooelogists that it is easy to overlook its importance.  His employment of the skeleton as the basis of classification was succeeded by the work of others who made a similar use of the muscular anatomy, of the intestinal canal, of the windpipe, of the tendons of the feet, and many other structures which display anatomical modifications in different birds.  The modern student finds that all these new sets of facts are much greater in bulk than the work of Huxley, and it is easy for him to remain in ignorance that they were all suggested and inspired by the method which Huxley employed.  He finds that further research has supplanted some of Huxley’s conclusions, and it is easy for him to remain in ignorance that the conclusions themselves suggested the investigations which have modified them.  Huxley’s anatomical work was essentially living and stimulating, and too often it has become lost to sight simply because of the vast superstructures of new facts to which it gave rise.

Closely associated with vertebrate anatomy is the subject of geographical distribution.  In 1857 the study of this important department of zooelogy was placed on a scientific basis, practically for the first time, by a memoir on the geographical distribution of birds published in the Journal of the Linnaean Society of London.  It was known in a general way that different kinds of creatures were found in different parts of the world, but little attempt had been made to map out the world into regions characterised by their animal and vegetable inhabitants, as the political divisions of the world are characterised by their different governments and policies.  Mr. Sclater, who two years later became secretary of the Zooelogical Society of London, in his memoir introduced the subject in the following words: 

“It is a well-known and universally acknowledged fact that we can choose two portions of the globe of which the respective fauna and flora shall be so different that we should not be far wrong in supposing them to have been the result of distinct creations.  Assuming, then, that there are, or may be, more areas of creation than one, the question naturally arises how many of them are there, and what are their respective extents and boundaries; or, in other words, what are the most natural primary ontological divisions of the earth’s surface?”

Mr. Sclater’s answer was that there are six great regions; Neotropical, Nearctic, Palaearctic, Ethiopian, Indian, and Australian, and his answer, with minor alterations and the addition of a great wealth of detail, has been accepted by zooelogy.