32 



DESIGN IN NATURE 



PLATE XVII 



Fig. 1. 



Fig. 2. 



Fig. 3. 



Fig. 4. 



PLATE XVI (continued) 



the tendrils of certain climbing plants ; tlie tnsks of the elephant and mammoth supplying examples of jjermanent spirals seen also in 

 teeth, horns, bones, &c. Drawn by C. Berjeau for the Author. 



Fig. 3. — View of spiral .shell {Mitra epinropalis), sawn throngh longitudinally, showing columella with right-handed spiral folds 

 (after Zittel). This affords the type of many spiral staircases. 



Fig. 4. — A. Spiral tusk of narwhal (Monodon monoceros). The tusk forms a left-handed spiral composed of several strands and 

 producing a symmetrical combination. This is one of the largest examples of a spiral tooth. B. A portion of the same on a largei' scale. 



Pig. 5. — Spiral annulated horn of the addax (Addax nasomaculatus). The line a, h shows the amount of spirality. 



Fig. 6. — Primary feather of the wing of the swan, seen from above and edgeways, to show the spiral nature of the feathers on 

 which flight mainly depends. 



A. Primary feather seen from above ; curves in every direction, a, b, Posterior margins ; c, d, anterior margins ; e, /, vane or 

 mid-rib ; c, g, double curve formed by the margins. 



B. The same feather, .seen edge-ways. Shows .spiral nature of feather, a, h, Posterior margin forming double curve arranged on a 

 different plane from anterior margin (c, d), which also forms a double curve. The two margins cross each other figure-of-8 fashion • 

 e,f, vane of feather. A primary feather is, in a way, a diminutive and perfect wing. Drawn from nature by the Author. 



Fig. 7. — The cloth moth with spiral proboscis. Drawn by 0. Berjeau for the Author. 



Fig. 8.— Lateral view of the nautilus in its shell (after Owen). Shows exquisite right-handed spiral, a. Tentacles • b hood • 

 c, mantle ; rf, funnel ; e, eye ; /, .siphuncle ; ff, compartment of shell. 



