430 ON CONCRETIONS, SPICULES, ETC. [ch. 



or arborescent shapes so frequently seen in microscopic crys- 

 tallisation. 



To return to Liesegang's rings, the typical appearance of 

 concentric rings upon a gelatinous plate may be modified in 

 various experimental ways. For instance, our gelatinous medium 

 may be placed in a capillary tube immersed in a solution of the 

 precipitating salt, and in this case we shall obtain a vertical 

 succession of bands or zones regularly interspaced : the result being 

 very closely comparable to the banded pigmentation which we see 

 in the hair of a rabbit or a rat. In the ordinary plate preparation, 

 the free surface of the gelatine is under different conditions to the 

 lower layers and especially to the lowest layer in contact with 

 the glass ; and therefore it often happens that we obtain a double 

 series of rings, one deep and the other superficial, which by 

 occasional blending or interlacing, may produce a netted pattern. 

 In some cases, as when only the inner surface of our capillary 

 tube is covered with a layer of gelatine, there is a tendency for 

 the deposit to take place in a continuous spiral line, rather than 

 in concentric and separate zones. By such means, according to 

 Kiister * various forms of annular, spiral and reticulated thickenings 

 in the vascular tissue of plants may be closely imitated ; and he 

 and certain other writers have of late been incUned to carry the 

 same chemico-physical phenomenon a very long way, in the 

 explanation of various banded, striped, and other rhythmically 

 successional types of structure or pigmentation. For example, 

 the striped pigmentation of the leaves in many plants (such as 

 Eulalia japonina), the striped or clouded colouring of many 

 feathers or of a cat's skin, the patterns of many fishes, such for 

 instance as the brightly coloured tropical Chaetodonts and the like, 

 are all regarded by him as so many instances of "diffusion-figures" 

 closely related to the typical Liesegang phenomenon. Gebhardt 

 has made a particular study of the same subject in the case of 

 •insects t- He declares, for instance, that the banded wings of 

 Papilio podalirius are precisely imitated in Liesegang's experi- 

 ments ; that the finer markings on the wings of the Goatmoth 

 {Cossus Ugni/perda) shew the double arrangement of larger and of 



* Ue.ber Zonenbildung in kolloidalen Mediev, Jena, 1913. 

 t Vcrh. d. d. Zool. Gesellsch. p. 179, 1912. 



