28 



DESIGN IN NATURE 



PLATE XIII 



/^Lrrt/tflo/tfnji 



Fig. 2. 



Plate xiii. illustrates spiral formations in shells. 



Fig. 1. — Spiral Fovaminireva after Brady. Challenyer Reports, vol. ix. In estimating the direction of the spirals in these 

 shells the spirals are traced from without inwards, or from base to apex (the Author). 



A. Discorbinc^ exiwia, x 35 ) Chambord right-handed spiral shells. 



B. Discm-lma Inconcava, x 45. ( ° ^^ 



C. Galcarina defrancii, x 20. Spiculated left-handed spiral shell. 



D. Gristdlaria calcar, x 35. Curious plicated left-handed spiral shell. 



E. OrUculina adimai, x 20. Symmetrical shell with left-handed spiral whorl at apex. Resembles spiral nebulae (Plate viii.), 

 certain spiral cones (Plate xi.. Fig. 1, lower row), and spiral cast of heart (Plate xvii., Fig. 3, B). 



F. Oristellaria orbicularis, x 20. 



G. C'ristellaria vortex, x 20. F and G are symmetrical shells with ri.L'ht-handed spiral whorls at apex. They resemble nebulfB 

 (Plate viii., Fig. 4); spiral seeds (Fig. 11, D, E) ; spiral spermatozoon (Plate xii., Fig. 1, E) ; and the spiral apex of the heart 

 (Plate xvii., Fig. 3, A). 



H. AmiiioiHscus tenuis, x 12. C'renated right-handed spiral shell with many and fine convolutions. 



Fig. 2. — A. Mesial line section of shell of Nautilus (Nautilus pompilius). Forms an excpiisile left-handed spiral, with beautiful 

 curved partitions becoming smaller as the apex of the shell is approached. Nothing can exceed the grace and beauty of the section 

 here exhibited. 



B. Rlujssota brookei. Forms right-handed spiral. 



C. Acavus plmnix (white variety). Forms left-handed spiral. 



D. Strophocheilus {Bonis) ohlongus. Forms left-handed spiral. 



E. Gceloceras (Ammonites) commnnis. Fo.ssil, Upper Lias formation. J. Scoresby. Forms a striking, closely-coiled, right-handed 

 spiral. 



F. Scalaria scalaris. Forms a beautiful pyramidal, spirally-ornamented, left-handed spiral. 



G. Eburna spirata. Forms a finely-marked left-handed spiral. 



Drawn by C. Berjeau from ]>hotogra|jhs by the Author, 



