THE EVOLUTION OF CONTINUITY 163 



and the water-pressure would make for rest in situ of the 

 zygote and its division results, and conceivably for attach- 

 ment. The result of attachment would presumably be 

 proximal cell-arrest, with distal cell-multiplication and serial 

 growth. But there is reason to suppose that as cell succeeded 

 cell there would be a slight diminution in density, with 

 a resultant slight pull towards the surface of the water. 

 Light-attraction might also act by stimulating distal growth 

 and drawing the filament towards the surface. 



This supposed diminution in density is not fanciful, 

 for it obviously occurs in the development of present-day 

 algse such as Spirogyra, whose zygote develops in under- 

 water attachment, and whose filament floats to the surface. 

 Another example is the bladder-wrack, which, attached 

 to some rock or stone, strains towards the surface when 

 submerged ; diminishing density here taking the special 

 form of air-floats. Hydrozoal colonies, and stalked crinoids, 

 are other examples of organisms whose zygotes are denser 

 than the water, and in whose development diminishing 

 density may be presumed from the fact that growth is upwards 

 and away from attachment. Naturally, in the sudden 

 evolution of filamentous growth we presume a very faint 

 diminution of density with extension ; just sufficient to 

 cause upward growth in face of even lateral water-pressure. 



In the evolution of the zooid we have to presume 

 that a fertilised ovum, or its equivalent, with filamentous 

 potentialities, came to develop in water-pressure conditions 

 severe enough to institute a higher form of Continuity ; 

 the result being, on the whole, as if several beginnings of 

 branching filaments were squeezed together, as they grew, 

 into a little mass by water-pressure. If the multiplying 

 cells of such a mass regularly diminished in density, a spherical 

 form, then a pear-shaped one, and finally a cylindrical form, 

 could result, as accompaniments of upward growth. Another 

 result of gradual diminution in cell-density could be the 

 formation of a hollow interior in the mass. 



In this connection it may be noted that if a liquid heavier 

 than water — chloroform, for example — be placed in small 

 amount under water, it takes the form of one or more discrete 

 flattened globes. Gravity and overlying pressure try to 

 spread the chloroform out as a film on the bottom, but lateral 



