THE BEGINNINGS OF LIFE. 559 



is seen to be so intimate — the transitions are so rapid 

 and irregular in their actual course on different occasions 

 — that we cannot now look upon them as representing 

 distinct ^ species ^ although each of them may be per- 

 fectly capable of ^ breeding true ' on one or more occa- 

 sions. Neither do the several forms occur in regularly 

 recurring groups, so as to enable us to say that such 

 and such varieties are mere developmental stages of 

 one and the same ultimate form^. It is, therefore, 

 on this account, and because nothing answering to 

 those regular assemblages of definitely recurring forms 

 which we include under the word <^ species' exists 

 amongst them, that I propose, henceforth, to speak of 

 such evanescent and transitory organisms as ^Ephemero- 

 morphs/ In the main, they are forms of Life whose 

 motto might fitly enough be found in these words from 

 Ovid :— 



'Corpora vertuntur; nee quod fuimusve, sumusve, 

 Cras erimus.' 



Some of them, however, are organisms which may per- 

 sist in the same condition for a very considerable period. 

 This, for instance, is notably the case with certain 

 varieties of Lichen which often live for a very long 

 period^. But in other cases the forms only appear to 



^ Although this is the case occasionally with some forms — as when 

 some few out of countless multitudes of Bacteria develop through Vibrio 

 and Leptothrix forms into Fungi. Here it stops, however, for there is no 

 normal production of Bacteria from the simple Fungi. 



a Thus the Rev. M. J. Berkeley says :— ' Some of the large patches of 

 Parmelia, which occur on rockS; are of very great age. Patches of such 



