62 DESIGN IN NATURE 



PLATE XL 



Plate x]. illustrates in a striking manner well-marked resemblances in inorganic and organic structures as 

 regards longitudinal cleavage and transverse cleavage or segmentation. 



Fig. J.— Photograph of Fingal's Cave, Staffa, in the west of Soothxnd. Consists of vertical basaltic columns largely hexagonal in 

 shape. They ave separated transversely at short intervals as in a vertebral column. 



Fig. 2. — Photiigraph of portion of the Giant's CaiLseway in the north of Ireland. The columns resemble those found in Fingal's 

 Cave (Fig. 1 of this Plate). Figs. 1 and 2 of this Plate show the longitudinal and transverse cleavages in Plutonic rooks to perfection. 

 Similar cleavages are seen in hydrated starch (I'^ig. .3 of this Plate). They greatly resemble the cleavages observed in plants and 

 animals, especially the latter (Figs. .5, 6, 7, and 8 of this Plate), and point to a law of development or differentiation common to the 

 inorganic and organic kingdoms (the Author). 



Fig. 3. — Pentagonal and hexagonal prismatic columns resembling those found in Fingal's Cave and the Giant's Causeway, 

 produced artificially by evaporating and desiccating a fluid mixture of starch (the Author). 



Fiu. 4. — Fossil coral (Lithostrotion hasaltifonne) found in England, Ireland, Russia, Io«-a, and westward of the Mississippi 

 (D. D. Owen). Shows beautiful prismatic, hexagonal columns, wonderfully reseiriljliug the basaltic rock columns found in Fingal's Cave 

 and Giant's Causeway (Figs. 1 and 2 of this Plate), which I have shown can be produced artificially (Pig. 3 of this Plate). 



Fig. 5. — Fin or wing of the sturgeon (Acipeiiser), (after Giinther). Displays well-marked longitudinal cleavage with a certain 

 amount of transverse cleavage, c, e, d, Root and thick, tapering semi-rigid margin of fin ; /, thin, elastic margin of fin. The 

 triangular shape and graduated structure of the fin furnish the type for all propelling fins and wings — fins and wings having much 

 in common, the latter being larger. 



Fig. 6. — Fore-limb of Ceratodus, a member of a family of very ancient fishes, dating back to the Triassic and Jurassic eras, and 

 still surviving in Australian waters (after Giinther), Shows typical radiating, branching, segmented arrangements. The fore-limb 

 forms a paddle rather than a fin or wing. It is not graduated, as in Fig. 5, to form a ]jropelIing organ. «, h, Root of fore-limb ; 

 c, broad basal cartilage supporting tapering segmented axis and diverging rays ; d, tip of fore-limb ; e, anterior, and /, posterior 

 margins of same. 



Fig. 7. — Trilobite (llomulonotus delphinocepludas), (after Nicholson). Shows transverse cleavage or segmentation. 



Fig. 8. — Human vertebral column or backbone (after Holden). Shows branching and typical transverse cleavage or segmentation. 

 Compare with Fig. 7 of this Plate, and with the figures of Plate xxxix. The alternating curves presented by the backbone form a 

 veritable line of beauty. 



Fig. 9. — A young coral {Luusdaleia flun'/ormix) with buds or corallites on the disc, illustrating calycular gemmation (M. Edwards). 



HEXAGONAL STRUCTURES 



In the United Kingdom and in almost every country in Europe igneous rocks occur. They do not necessarily 

 form hills with cones and craters indicating their origin. Thus the rocks of Stafia in Scotland and the Giant's 

 Causeway in Ireland are called basalt, and are known to be volcanic, as they agree in their columnar prismatic 

 structure and mineral composition with the lava which has flowed from the craters of volcanoes. The remarkable 

 structure of these rocks is supposed to be due to shrinkage and consohdation on coohng. Similar columnar pris- 

 matic structures are produced when a mixture of hydrated starch is slowly dried off in the sun or in an oven. In 

 both cases the columns, generally pentagonal or hexagonal in shape, are divided transversely at more or less 

 regular intervals.^ 



I direct attention to the basaltic prismatic columns as the longitudinal and transverse cleavages and hexagonal 

 outline which they reveal re-appear in many living plant and animal structures. The longitudinal and transverse 

 cleavages are seen in the Equisetacea), in cones and branches among plants, and in the segmented animals with limbs, 

 bronchial tubes, &c. The hexagonal formations are witnessed in epithelial and liver cells, in scales and coverings, 

 in transverse sections of fascicuh of muscle, in the enamel of teeth, in the honeycomb, in old-world corals, &c. 

 A familar and striking example {Eunomia radiata) occurs in the coralline limestones. This is found in the Great 

 OCihte, near Bath, where it is very conspicuous ; single individuals forming masses several feet in diameter, and 

 which probably required centuries for their formation. Another good example (Favosites cervicornis) is met with 

 in large numbers in the Devonian and Silurian groups, in the great limestones of Plymouth and Torbay. An 



'■ The I'ollowiug is the account given of these curious and interesting structures by Sir Charles Lyell : " One of the characteristic forms of 

 voletuiic rocks, especially of ba.salt, is the colunuiar, whei-e large masses are divided into regular prisms, sometimes easily separable, but in other 

 eases adhering firndy together. Tlie colunuis vary in the number of angles, from three to twelve ; but they have most commonly from five tn 

 seven aides. They are often divided transversely, at nearly equal distances, like the joints in a vertebral column, as in the (Uant's Causeway in 

 Ireland. Tliey vaiy exceedingly in resjject to length and diameter. Dr. MacCuUoch mentiims some in Skyc which are about 400 feet long ; 

 othei's, in Morveu, not exceeding an inch. In regard to diameter, those of Ailsa measure 9 feet, and those of Morven an inch or less. They 

 are usually straight, but sometimes curved ; and examples of both these occur in the island of Statfa. In a horizontal bed or sheet of trap the 

 colunuis are vertical ; in a vertical dike they are horizontal." 



