This is precisely what we do find; and, moreover, we sometimes get a very fair drawing of the important hidden parts, even where least expected, as in a cat's head, a snake's body, a dragon-fly's thorax, a spider's abdomen, a bird's skull. But if animals thus learned to paint themselves in definite patterns, we might expect that when called upon to decorate _for the sake of beauty_ certain parts not structurally emphatic, they would adopt well-known patterns, and hence arose the law of repetition. But with wider experience came greater powers, and the necessity for protection arising, the well-known patterns were enlarged, till an uniform tint is produced, as in the Java pig, or some repeated at the expense of others, as in the civets. But so ingrained is the tendency to structural decoration that even where modification has reached its highest level, as in the leaf-butterflies, some trace of the plan that the new pattern was founded on is recognisable, just as the rectangular basis can be traced in the arabesque ornaments of the Alhambra. The pointing out of this great fact has seemed to us a useful addition to the great law of evolution. It supplements it; it gives a reason why. Could he who first saw these points have read these final pages, it would have lightened the responsibility of the one upon whom the completion of the work has fallen. But he died when the work was nearly finished. The investigation is of necessity incomplete, but nothing bears such misstatements as truth, and though specialists may demur to certain points, the fundamental arguments will probably remain intact. [Illustration: FINIS.] GLOSSARY. ACETABULA. Lat. _acetabulum_, a little vessel. Sucking discs as on the tentacles of _Physalia_. AORTA. Gr. The chief artery. CEPHALOTHORAX. Gr. _kephale_, head; _thorax_, chest. The anterior division of the body in Crustacea and Arachnida, composed of the amalgamated segments of the head and thorax. CILIA. Lat. _cilium_, an eyelash. Microscopic filaments having the power of vibratory movement. C[OE]NOSARC. Gr. _Koinos_, common; _sarx_, flesh. The common stem uniting the separate animals of compound hydrozoa, &c. CORPUSCLE. Lat. _corpusculum_, a little body. Small coloured bodies, as in the endoderm of hydra, p. 59. DIFFERENTIATED. Modified into definite organs, or parts; as distinct from structureless protoplasm. ECTODERM. Gr. _ektos_, outside; _derma_, skin. The internal layer or skin of the Coelenterata. EFFERENT. Lat. _effero_, to carry out. A vessel which carries fluids out of the body is said to be efferent. ENDODERM. Gr. _endon_, within; _derma_, skin. The inner layer or skin of Coelenterata. _See_ ECTODERM. ENDOSARC. Gr. _endon_, within; _sarx_, flesh. The inner layer of sponges.