THE BEGINNINGS OF LIFE. 221 



On the tenth day, similar though more advanced 

 changes were seen. Although the majority of the 

 Amoebse were still active and polymorphic, hundreds of 

 them were becoming encysted, and the different stages 

 of the process could be well seen. They were these : — 

 The previously spherical Amoeba lost their vacuoles, 

 the granules almost wholly disappeared, and the body 

 generally became slightly refractive — the nucleus being 

 still visible. After a time the nucleus became invisible, 

 and the whole substance of the organism assumed a 

 homogeneous and highly refractive appearance — so that 

 when it was examined a little beyond the focal dis- 

 tance it looked almost like an oil globule. There was 

 a decided condensation, also, of the outer layer of 

 protoplasm, this being the first trace of the cyst-wall. 

 Subsequently the cyst-wall became more and more 

 manifest, whilst the size of the sphere slightly dimi- 

 nished, and assumed a faintly brownish tinge. From 

 the surface of the developing cyst there were a number 

 of very short, ray-like projections (Fig. 58,^). In the last 

 stage, whilst the cyst-wall became more developed and 

 the projections more obvious, the whole exterior en- 

 velope assumed a decidedly brown colour, and the con- 

 tained protoplasmic mass, which had again become less 

 refractive, distinctly separated from the cyst-wall ^ 



^ In the course of the next few days myriads of the Amoebae had 

 undergone this kind of change, which is inevitable as soon as the activity 

 of their vital processes becomes diminished. It is the extraordinary 

 molecular activity and constant change of shape of the Amoebae which 

 tends to prevent the earlier occurrence of this primary differentiation. 



