314 SCIENCE PROGRESS. 



an emanation of specialised biophors from the nucleus into 

 the cytoplasm, there is a general agreement that the co- 

 operation is of the nature of a complex exchange of 

 chemical material. If this be the case, the rate of exchange 

 must be the measure of vital activity, and it is clear that 

 the rate of exchange will be greatest in immediate proximity 

 to the nucleus and will become increasingly less the greater 

 the distance from the nucleus. At a certain distance, which 

 might be called the limit of nuclear influence, the rate of 

 exchange will be reduced to zero. We see that in the 

 protozoa the forms which have a single nucleus are small, 

 and we may say, in consequence of the foregoing- considera- 

 tions, that their size is determined by the limits of nuclear 

 influence. But many protozoa are multinuclear, and I 

 believe that there is no exception to the rule that protozoa 

 of relatively large size are also multinuclear. Such is 

 obviously the case in such forms as Radiolaria, Actino- 

 sphserium, Pelomyxa, the Myxomycetes and others. From 

 a consideration of all the facts of the case we may legiti- 

 mately infer that in any given biont growth beyond 

 certain limits is incompatible with a uninuclear condition, 

 and that further growth involves multiplication of the 

 nucleus, which may have as consequences: (i) discon- 

 tinuous growth, which in its simplest form is reproduction 

 by binary fission : (2) continuous growth, in which the 

 nucleus is multiplied so that all parts of the enlarged cyto- 

 plasm may receive an equal share of nuclear influence. 

 There are numerous cases in which, as I pointed out before, 

 the two conditions are combined. There is a ccenocytial r 

 stage of considerable duration, followed by reproduction 

 (or discontinuous growth). 



The next phase is the formation of a biont of consider- 

 able size, in which very numerous nuclei are arranged in 

 definite manner in a continuous mass of protoplasm. Such 

 a condition is represented by the Cceloblastas, and also in the 



1 When in my earlier essay I coined the word hypopolycytial I was 

 not aware that Professor Vines had applied the term ccenocytial to the 

 Cceloblastse. His term has the priority and is more euphonious, so I adopt 

 it instead of my own. 



