In the present revised two volumes several changes were made for the inclusion of the elements of a classification under each illustration of a whole, or almost whole, animal. This may help the student more or less painlessly to familiarize himself with the animal's systematic position.
There can be little doubt that the study of zoology is most profitably as well as most pleasantly begun in the field and by the sea-shore, in the zoological garden and the Aquarium. In a very real sense, it is true that the best zoologist is he who knows the most animals, and there can certainly be no better foundation for a strict and scientific study of the subject than a familiarity with the general appearance and habits of the common members of the principal animal classes.
There can be no question as to the vast improvement effected in zoological teaching by the practice of preceding the study of a given group as a whole by the accurate examination of a suitable member of it. With the clear mental image of a particular animal, in the totality of its organisation, the comparison of the parts and organs of other animals of like build becomes a profitable study, and the danger of the comparative method - that the student may learn a great deal of the systems of organs in a group without getting a clear conception of a single animal belonging to it - is much diminished.
A not uncommon method of expounding the Science of Zoology is to begin the study of a given group by a definition, the very terms of which it is impossible that the student should understand; then to take a general survey of the group, illustrated by casual references to animals and to structures of which it is highly unlikely he has ever heard, and, finally to descend to a survey of the most important forms included in the group.