274 BIOLOGY. [BOOK in. 



to death ; for putting aside for the present the cases of spon- 

 taneous generation with which we have not to occupy ourselves 

 here, every complex individual of the two organic kingdoms 

 springs from a simple cell. Growth can therefore be effected 

 only by an enormous multiplication of the anatomical elements. 

 This, in effect, is what happens. But as to the mode of genera- 

 tion of these histological elements, we find ourselves in the 

 presence of two great rival theories which we have already 

 signalised. The one more especially defended in Germany is the 

 theory of cellular generation. The other, maintained chiefly in 

 France by M. Ch. Robin and his school, is that of spontaneous 

 genesis. 



FIG. 39. 



"Reproduction by segmentation of an elementary organism, amoneron : A, entire moneron 

 (protamceba) ; J5, the same moneron divided into two halves by a median fissure ; C, the 

 two halves have separated, and constitute now independent individuals. 



According to the cellular theory, maintained in all its vigour 

 by M. Virchow, and still admitted by the majority of German 

 naturalists and physiologists, every cell comes directly and 

 strictly from a pre-existing mother cell. Omnis cellula e cellula ; 

 such is the formula which sums up the doctrine. Whatever 

 the biological process may be, simple division (Fig. 39), or the 

 budding from the mother cell, &c., there is always proliferation 

 alike in the animal kingdom and in the vegetal kingdom. 



The doctrine of spontaneous genesis is less exclusive. With- 

 out denying the fact of cellular proliferation, which is very 

 generally observed in the vegetal kingdom, at the outset of the 



