GROWTH, METAMORPHOSIS AND DEVELOPMENT 263 



It is easy to imagine that layered membranes develop by the re- 

 moval of a substance which holds another substance in solution. I 

 have experimented with this end in view by dissolving globulin in 

 gelatin containing sodium chlorid and layering water over it; when 

 the sodium chlorid diffused away, then the globulin precipitated 

 out. As a matter of fact no layered structures developed in the 

 gelatin but only turbidities uniformly distributed. This does not 

 by any means mean that, with a different arrangement of the ex- 

 periment, regular layered membranes might not be obtained. 



In organisms we frequently encounter stratified structures which, 

 in most cases, occur as the result of rhythmic deposition. The an- 

 nual rings of trees, the various layers in the otoliths of young and of 

 old fishes cannot be explained in any other way than that periods of 



FIG. 48. Starch granules. (Kilnitz-Gerloff.) 



rest follow periods of strong accretion. In contrast to these " external 

 rhythms" which obviously are induced by changing conditions affect- 

 ing an organ, there are also layered structures with "internal rhythms " 

 which suggest LIESEGANG' s rings As such, we must regard starch 

 grains (Fig. 48), the silicious, sponginous and calcareous structure of 

 sponges, and the perforated calcareous shells of the foraminifera and 

 many fish scales. R. LiESEGANG* 5 mentions in addition the con- 

 centric lamellae about the HAVERSIAN canals in the bones of verte- 

 brates, the rods of the retina and the spiral cross striae of muscle 

 fibers. W. GEBHARDT compares the rhythmic markings on butterflies' 

 wings to LIESEGANG structures. The coarse layers of the otoliths 

 of fishes, the annual rings of trees, the concentric structure of pearls 

 are penetrated by still finer layers, whose formation R. LIESEGANG 

 thinks is analogous to the formation of the rings he described. 



