266 



THE FORMS OF CELLS 



[CH. 



in all directions ; in other words it will tend to be set normally 

 to the surface of the sphere, that is to say radiating directly 

 outwards from the centre. If the distance between two adjacent 

 filaments be considerable, the curve will simply meet the filament 

 at the angle a already referred to ; but if they be sufficiently near 

 together, we shall have a continuous catenary curve forming a 

 hanging loop between one filament and the other. And when this 

 is so, and the radial filaments are more or less symmetrically 

 interspaced, we may have a beautiful system of honeycomb-like 

 depressions over the surface of the organism, each cell of the 

 honeycomb having a strictly defined geometric configuration. 



In the simpler Eadiolaria, the spherical form of the entire 

 organism is equally well-marked ; and here, as also in the more 

 complicated Heliozoa (such as Actinosphaerium), the organism is 



Fig. 90. A, Trypanosoma tineae (after Minchin); B, Spirochaeta anodontae 

 (after Fantham). 



differentiated into several distinct layers, each boundary surface 

 tending to be spherical, and so constituting sphere within sphere. 

 One of these layers at least is close packed with vacuoles, forming 

 an "alveolar mesh work," with the configurations of which we shall 

 attempt in another chapter to correlate the characteristic structure 

 of certain complex types of skeleton. 



An exceptional form of cell, but a beautiful manifestation of 

 surface-tension (or so I take it to be), occurs in Trypanosomes, those 

 tiny parasites of the blood that are associated with sleeping- 

 sickness and many other grave or dire maladies. These tiny 

 organisms consist of elongated solitary cells down one side of which 

 runs a very delicate frill, or "undulating membrane," the free 

 edge of which is seen to be slightly thickened, and the whole of 



