270 THE BEGINNINGS OF LIFE. 



as Cohn 1 thinks, the later free-swimming stage in the 

 existence of certain algae, intermediate between Pal- 

 mell<e and Oscillator!* ; or lastly (4) that they are 

 the first and most common developmental phase of 

 newly- evolved specks of living matter, which are capa- 

 ble, either singly or in combination, of developing into 

 many different kinds of living things. 



Ehrenberg's is an almost obsolete point of view. 

 Bacteria are no more animal than vegetal organisms 

 they are protists. And few even of the firmest believers 

 in the constancy of specific forms would now be in- 

 clined to maintain this doctrine with respect to Bacteria. 

 The opinions of Hallier and Cohn will be again referred 

 to in other portions of this chapter. 



I have been compelled to take the fourth view, 

 and to look upon plastide-particles as the mere tem- 

 porary and initial developmental form of many or- 

 ganisms which may afterwards present distinct cha- 

 racteristics of their own 2 , though certain of these 

 particles may, through default of the necessary con- 

 ditions, never actually develop into higher modes of 

 being. But a very large number of them undoubtedly 

 give rise to the bodies known as Bacteria, by a direct 

 process of growth and development. These Bacteria 

 vary very considerably in size, and also in the 

 quality of their movements. Their sifce seems to 



1 ' Entwickelungs-geschichte der Mikroscop.' Algen und Pilze, 1854. 



2 Many of what may seem to be mere plastide-particles, are only 

 Bacteria seen endwise. 



