252 CLASSICS OF MODERN SCIENCE 



bolic phenomena (to metaholikon, implying that which is Hable to 

 occasion or to suffer change). 



The general plastic appearances in the cells are, as we have seen, 

 the following: at first a minute corpuscle is formed (the nucleolus) ; 

 a layer of substance (the nucleus) is then precipitated around it, 

 which becomes more thickened and expanded by the continual dep- 

 osition of fresh molecules between those already present. Deposition 

 goes on more vigorously at the outer part of this layer than at the 

 inner. Frequently the entire layer, or in other instances the outer 

 part of it only, becomes condensed to a membrane, which may con- 

 tinue to take up new molecules in such a manner that it increases 

 more rapidly in superficial extent than in thickness, and thus an inter- 

 vening cavity is necessarily formed between it and the nucleolus. 

 A second layer (cell) is next precipitated around this first, in which 

 precisely the same phenomena are repeated, with merely the difference 

 that in this case the processes, especially the growth of the layer and 

 the formation of the space intervening between it and the first layer 

 (the cell-cavity), go on more rapidly and more completely. Such 

 were the phenomena in the formation of most cells; in some, how- 

 ever, there appeared to be only a single layer formed, while in others 

 (those especially in which the nucleolus was hollow) there were three. 

 The other varieties in the development of the elementary parts were 

 (as we saw) reduced to these — that if two neighbouring cells com- 

 mence their formation so near to one another that the boundaries of 

 the layers forming around each of them meet at any spot, a common 

 layer may be formed enclosing the two incipient cells. So at least 

 the origin of nuclei, with two or more nucleoli, seemed explicable, by 

 a coalescence of the first layers (corresponding to the nucleus), and 

 the union of many primary cells into one secondary cell by a similar 

 coalescence of the second layers (which correspond to the cell). 

 But the further development of these common layers proceeds as 

 though they were only an ordinary single layer. Lastly, there were 

 some varieties in the progressive development of the cells, which were 

 referable to an unequal deposition of the new molecules between those 

 already present in the separate layers. In this way modifications of 

 form and division of the cells were explained. And among the num- 

 ber of the plastic phenomena in the cells we may mention, lastly, the 

 formation of secondary deposits ; for instances occur in which one or 



