there is no homology between the wing of the bat and that of the flying-dragon, for the latter is formed of certain ribs, and not of limb bones.
Homology may be further distinguished into (1) a relationship which, on evolutionary principles, would be due to descent from a common ancestor, as the homological relation between the arm-bone of the horse and that of the ox, or between the singular ankle bones of the two lemurine genera, cheirogaleus and galago, and which relation has been termed by Mr. Ray Lankester "homogeny;"[[162]] and (2) a relationship induced, not derived—such as exists between parts closely similar in relative position, but with no genetic affinity, or only a remote one, as the homological relation between the chambers of the heart of a
bat and those of a bird, or the similar teeth of the thylacine and the dog before spoken of. For this relationship Mr. Bay Lankester has proposed the term "homoplasy."
"Serial homology" is a relation of resemblance existing between two or more parts placed in series one behind the other in the same individual. Examples of such homologues are the ribs,
or joints of the backbone of a horse, or the limbs of a centipede. The latter animal is a striking example of serial homology. The body (except at its two ends) consists of a longitudinal series of similar segments. Each segment supports a pair of limbs, and the appendages of all the segments (except as before) are completely alike.
A less complete case of serial homology is presented by Crustacea (animals of the crab class), notably by the squilla and by the common lobster. In the latter animal we have a