424 THE FORMS OF CELLS [ch. 



are sometimes finely beaded* ; and slight differences in the beading 

 and branching are said to characterise allied species of fish. Such 

 a barbel looks hke a jet or branching stream of one fluid falhng 



through another. It may indeed 

 be that in these quiet depths 

 growth easily follows its fines of 

 least. resistance, and that in the 

 shaping of these pecufiar out- 

 growths hydrodynamical and 

 capillary forces are taking the 

 upper hand. 



We have found it easy to illus- 

 trate the sphere, the cy finder and 

 the unduloid, three of the six 

 "surfaces of Plateau," all with 

 an endless wealth of illustration 

 among the simplest of organisms. 

 The plane we need hardly look 

 for among the finite outlines of a 

 fluid body; and the catenoid, also 

 *a surface of zero mean curvature, 

 can likewise only be a rare and 

 transitory configuration. One last 

 surface still remains, namely the 

 nodoid; and there also remains 

 one very common but most re- 

 markable Protozoan configura- 

 Fig. 139. Stentor, a cUiate infusorian: tion, that of the cifiate Infusoria, 



from Savile Kent. ii.i, ^.i, j. • ,.- r i. 



to the most characteristic leature 



of which we have not so far found a physical analogue. Here the 



curved contour seems to enter, re-enter, and disappear within the 



substance of the body, so bounding a deep and twisted space or 



passage, which merges with the fluid contents and vanishes within 



the cell, and is called by naturafists the "gullet." This very 



pecufiar and compficated structure is only kept in equifibrium, and 



in existence, by the constant activity of cifia over the general surface 



* See, for instance, C. Tate Regan and E. Trewavas on The Stomiatidae of the 

 Dana Expedition, 1930; W. Beebe, Deep-sea Stomiatoids, Copeia, Dec. 1833. 



