466 the president's address. 



distinct, but frequently run together, and that the best going is 

 sometimes to be found along one and sometimes along another. 



Starting along the morphological road Ave shall very soon find 

 that there are many grades or orders of individuality, and that 

 what constitutes a perfect individual in one case may by no 

 means do so in another. 



Amongst the lower forms of life the individual frequently 

 consists, as you know, of a single cell, a single nucleated mass 

 of protoplasm capable of performing by itself all those actions or 

 functions which are necessary for the maintenance of life. The 

 cell is, of course, frequently looked upon as the lowest structural 

 unit, and the unicellular plants and animals as individuals of the 

 first order. It may fairly be questioned whether this view is 

 strictly correct, for the nucleated cell has already progressed a 

 long way along the path of evolution, and it is quite conceivable 

 that it may have originated as a colony of individuals of a still 

 lower order micellae, plastidules, biophors, or whatever else we 

 like to call them ; while it is certain that some existing organisms, 

 such as the Bacteria, have not yet attained the level of perfect 

 cells. 



We know, however, that all the higher organisms actually 

 start life as single nucleated cells, formed usually by the union of 

 two gametes or germ cells, and that these germ cells themselves 

 originate as complete nucleated cells by the process of cell-division, 

 and not, so far as we can tell, by the multiplication and addition 

 of units of a lower order. This fundamental fact seems to justify 

 us in looking upon the cell as the lowest morphological unit, and 

 we may accordingly accept it as the starting-point for our inquiry. 



A unicellular organism, after attaining a certain size, and 

 under favourable circumstances, may divide into two parts which 

 completely separate from one another and form two new and 

 independent individuals. In this simple process of reproduction 

 the parent cell ceases to exist as an individual, but we cannot say 

 that it perishes, for its substance is merely divided between the 

 two daughter cells and there is nothing left over to die. 



In the multicellular animals and plants we meet with a very 

 different state of things. Here the individual is composed, not 

 of a single cell, but of a number of such cells, often amounting to 

 very many millions, all united together in one body. Moreover, 

 these cells are not all alike, but very variously differentiated 



