T94 / LIONEL TAYLER [September 



best chances of survival and adaptation, either to old or to new con- 

 ditions, would be through conjugation. Selection would therefore 

 favour conjugation (Weismann). 



3. If for some reason, possibly nutritional in origin, fission in an 

 organism had not been quite complete, and the cells instead of separat- 

 ing had remained together, then as each new division reached maturity 

 it would divide and the process of division would continue till in- 

 terfered with by some outside condition, many different forms of these 

 masses of cells would thus be produced, examples of which may be 

 found in the different forms of sponges. Now, if for any reason a 

 curved single layer of cells was formed, it would go on growing in 

 all directions until it met other cells of the same collective cell 

 colony ; a multicellular growth limit would thus be reached. Now, 

 assuming this growth capacity to remain constant, one of three things 

 can happen. With a somewhat irregular hollow sphere of cells, it 

 would be conceivable that: (1) a bending in at one of the weaker 

 points, or (2) a bending out would occur, many cells being involved 

 in this yielding; or (.">) each cell might bud off a certain portion in- 

 dependently. Of the first or outward yielding, and the formation of 

 buds, we have many examples occurring in nature, as, for example, 

 bud development in the hydra ; of the inward yielding, the passage 

 from the blastoderm to the gastrula stage, through the process of 

 invagination occurring in the development of many animals, affords an 

 example of the second means of satisfying this growth tendency ; 

 while in the third case division of the individual cell, and separation 

 from its parent tissue, occurs in the formation of red blood corpuscles 

 in mammals, etc. 



4. It is obvious that the general structure of the organism would 

 be least disturbed by each individual cell throwing off buds, and 

 therefore the more specialised the organic structure the less likelihood 

 of those organisms that reproduced by any collective alteration of the 

 the organism surviving. With growing specialisation each tissue will 

 become less and less able to reproduce other than its own specialisa- 

 tion, hence reproduction will occur only when the buds from the 

 requisite differentiations meet ; now in the case of the hydra it 

 appears to be only necessary to have representatives of two classes of 

 cells, the ecto- and entoderm, and these thrown-off portions of cell 

 structure would, when the requisite number met, owing to perhaps 

 some stronger growth tendency, tend to push up the cells above them, 

 and as the most likely place for the ectoderm and entoderm units to 

 meet would be hetwcen these two layers, we should expect develop- 

 ment to commence from this position. With increasing differentia- 

 tion reproductive centres would tend more and more to be localised 

 to one centre. Hence with increasing specialisation there would be 

 progressively less power of local or somatic reproduction. 



5. A special kind of organism survives for two reasons: (1) 



