564 THE BEGINNINGS OF LIFE. 



the parent form. And where development takes place 

 by such successive stages which, as it were, reproduce 

 or copy previous current heterogenetic changes the 

 same tendency to multiply by an asexual process is 

 manifested by the several forms which represent the 

 different developmental stages, as was previously dis- 

 played by the several heterogenetic products. 



Heterogenesis, therefore, would thus appear to be 

 the essential underlying cause of all developmental 

 transformations or metamorphoses j and, moreover, 

 the hitherto unexplained phenomena of c alternate 

 generation' may, perhaps, be deemed to receive a 

 rational and approximate interpretation 1 . 



1 There would thus be three distinct modes by which sexual repro- 

 duction may make its appearance amongst the ' Ephemeromorphs ' : 



(a) It may occur as it were ' accidentally,' at long and altogether 

 irregular intervals, during some of the later stages in a series of ephe- 

 meromorphic developments and then in a very rudimentary manner. 

 The best instances of this are, perhaps, to be found amongst Fungi. 

 Thus I would suggest that a relationship of this kind probably obtains 

 between Uredo, yEcidium, and Uromyces as a possible final form in 

 which rudimentary sexual organs may become differentiated. 



(6) It may occur, similarly, in one of the later stages of a series of 

 ephemeromorphic transformations, though such changes may subse- 

 quently tend to recur so as to produce a case of cyclical or ' indirect ' 

 homogenesis. Portions of ephemeromorphic life are, as it were, thus 

 nipped off and preserved, so as to constitute the different kinds of 

 ' alternate generation ' which are known to prevail both amongst animal 

 and vegetal forms of life. 



(c) It also occurs when an ephemeromorphic series ends abruptly 

 i. e. when by some final process of heterogenesis an organism is at 

 once produced which subsequently develops sexual characters, and 

 thenceforth multiplies by the homogenetic method. In this case the 



