386 



THE FOKMS OF TISSUES 



[CH. 



that a mathematical study of these, including an investigation of 

 the "deformation" of the wing (that is to say, of the changes in 

 shape and changes in the form of its "cells" which it undergoes 

 during the hfe of the individual, and from one species to another) 

 would be of great interest. In very many cases, the entomologist 

 relies upon this venation, and upon the occurrence of this or that 

 intermediate vein, for his classification, and therefore for his 

 hypothetical phylogeny of particular groups; which latter pro- 

 cedure hardly commends itself to the physicist or the mathe- 

 matician. 



Another case, geometrically akin but biologically very 

 different, is to be found in the httle diatoms of the genus Astero- 

 lampra, and their immediate congeners*. In Asterolampra we 



A B c 



Pig. 171. (A) Asterolampra inarylandica, Ehr. ; (B, C) A. variabilis, Grev. 

 (After Greville.) 



have a little disc, in which we see (as it were) radiating spokes of 

 one material, alternating with intervals occupied on the flattened 

 wheel-like disc by another (Fig. 171). The spokes vary in number, 

 but the general appearance is in a high degree suggestive of the 

 Chladni figures produced by the vibration of a circular plate. 

 The spokes broaden out towards the centre, and interlock by 

 visible junctions, which obey the rule of triple intersection, and 

 accordingly exemplify the partition-figures with which we are 

 dealing. But whereas we have found the particular arrangement 

 in which one cell is in contact with all the rest to be unstable, 

 according to Roux's oil-drop experiments, and to be conspicuous 



* See Greville, K. R., Monograph of the Genus Asterolampra, Q.J. M.S. vin, 

 (Trans.), pp. 102-124, 1860; of. ibid, (n.s.), ii, pp. 41-55, 1862. 



