280 THE INDUCTIONS OF BIOLOGY. 



valent, free-swimming, gametes replaced by sexually dif- 

 ferentiated sperm- and germ-cells, in some cases arising in 

 different organs set apart for their production, and essentially 

 representing those found in the higher plants. Transitional 

 forms, intermediate between these and the cases where 

 equivalent gametes are formed from any cell of the plant are 

 also known." 



Eecent investigations concerning the conjugation of Fro- 

 tozoa have shown that there is not, as was at one time thought, 

 a fusion of two individualities, but a fusion of parts of their 

 nuclei. The macro-nucleus having disappeared, and the 

 micro-nucleus having broken up into portions, each individual 

 receives from the other one of these portions, which becomes 

 fused with its own nuclear matter. So that even in these 

 humble forms, where there is no differentiation of sexes, the 

 union is not between elements that have arisen in the same 

 individual but between those which have arisen in different 

 individuals : the parts being in this case alike. 



The marvellous phenomena initiated by the meeting of 

 sperm-cell and germ-cell, or rather of their nuclei, naturally 

 suggest the conception of some quite special and peculiar 

 properties possessed by these cells. It seems obvious that 

 this mysterious power which they display of originating a 

 new and complex organism, distinguishes them in the 

 broadest way from portions of organic substance in general. 

 Nevertheless, the more we study the evidence the more are 

 we led towards the conclusion that these cells are not 

 fundamentally different from other cells. The first 



fact which points to this conclusion is the fact recently 

 dwelt upon (§ 63), that in many plants and inferior animals, 

 a small fragment of tissue which is but little differentiated, 

 is capable of developing into an organism like that from 

 which it was taken. This implies that the component units 

 of tissues have inherent powers of arranging themselves into 

 the forms of the organisms which originated them. And 

 if in these component units, which v/e distinguished as 



