180 THE INDUCTIONS OF BIOLOGY. 



contemplating these facts in connexion with various kindred 

 ones, there is suggested the hypothesis, that the form of each 

 species of organism is determined by a peculiarity in the con- 

 stitution of its units — that these have a special structure in 

 which they tend to arrange themselves ; just as have the 

 simpler units of inorganic matter. Let us glance at the evi- 

 dences which more especially thrust this conclusion upon us. 



A fragment of a Begonia-leaf, imbedded in fit soil and kept 

 at an appropriate temperature, will develop a young Bego- 

 nia ; and so small is the fragment which is thus capable of 

 originating a complete plant, that something like a hundred 

 plants might be produced from a single leaf. The friend to 

 whom I owe this observation, tells me that various succulent 

 plants have like powers of multiplication. Illustrating a 

 similar power among animals, we have the often-cited exper- 

 iments of Trembley on the common polype. Each of the 

 four pieces into which one of these creatures was cut, grew 

 into a perfect individual. In each of these again, bisection 

 and tri-section effected a like result. And so with their 

 segments, similarly produced, until as many as fifty polypes 

 had resulted from the original one. Bodies when cut off 

 regenerated heads ; heads regenerated bodies ; and when a 

 polype had been divided into as many pieces as was practica- 

 ble, nearly every piece survived and became a complete 

 animal. What, now, is the implication ? We 



cannot say that in each portion of a Begonia-leaf, and in 

 every fragment of a Hydra's body, there exists a ready- 

 formed model of the entire organism. Even were there 

 warrant for the now abandoned doctrine, that the germ of 

 every organism contains the perfect organism in miniature, it 

 still could not be contended that each considerable part of the 

 perfect organism resulting from such a germ, contains another 

 such miniature. Indeed the one hypothesis obviously nega- 

 tives the other. We have therefore no alternative but to 

 say, that the living particles composing one of these frag- 

 ments, have an innate tendency to arrange themselves into 



