224 THE BEGINNINGS OF LIFE. 



were generated by a most typical process of Hetero- 

 genetic Bioparadosis \ 



The changes which have been thus observed consti- 

 tute a very remarkable series. The simplest living 

 units (Bacteria] first swarm in the infusion- these be- 

 come aggregated at the surface so as to form a c pro- 

 ligerous pellicle/ in which embryonal areas gradually 

 appear ; as a result of segmentation in these embryonal 

 areas, specimens of Monas lens^ ^oV' i n diameter, more 

 or less suddenly make their appearance ; they increase 

 in size, occasionally assume an amoeboid appearance 

 for a time, and are ultimately transformed into real 

 Amoebae. The transition is effected by the loss of the 

 flagellum, the appearance of vacuoles in their interior, 

 and the simultaneous manifestation of polymorphism 

 and a creeping mode of progression ; at the same time 

 a nuclear corpuscle develops in the interior, and the 

 whole animal grows considerably. At last the Amoebx 

 gradually cease to exhibit their characteristic move- 

 ments, whilst they become more or less spherical and 

 motionless. Ultimately a firm bounding membrane is 

 produced, and they pass into the encysted condition, 

 in which, although slightly smaller in size, they consti- 

 tute spherules 15 1 50 // in diameter. On the removal of 

 some of this pellicle to the surface of a fresh infusion, 

 the Monads and Amoebse greatly increased in size ; all 

 the Monads gradually became converted into Amcebas, 

 and some of these at first went through the ordinary 

 1 See vol. i. p. 234. 



