THE BEGINNINGS OF LIFE, 561 



become more and more complex. But in conse- 

 quence of those laws of '^polarity/ upon which the 

 form of the simple organism depends, almost any 

 portions of such organisms, when once they are sepa- 

 rated by fission or gemmation, grow more or -less 

 immediately into similar organic forms ^. They ^ breed 

 true ' in all their stages — ^just as a separated fragment 

 of a crystal, when it remains immersed in the mother- 

 liquor^ will form the starting-point of another similar 

 crystal. So that where, in the case of the ephemero- 

 morph, the parent form has been attained by a con- 

 tinuous process of growth and development, we find 

 that the spore or <^ gemma' which is ultimately thrown 

 off tends again to go through a similar series of changes. 

 This may be seen in the development of a Fungus- 

 con idium or spore into a form similar to that from 

 which it had separated But where a succession of 

 forms has been produced, oti^ out of another, by 

 the occurrence of several successive, though ^ acci- 

 dental,' heterogenetic transformations, — any portion 

 cast off from the ultimate form is apt usually at once 

 to develop into an organism similar to that ultimate 

 form, rather than to reproduce the series of changes by 

 which it may have arisen. An Oxytricha or a Vorti- 

 cella, for instance, which may have been produced by 

 the transformation of a Euglena or other algoid vesicle, 

 multiplies its own form by fission or by the process 

 of gemmation • and should the Vorticella encyst itself, 



1 See p. 88. 

 VOL. II. O O 



