248 Prof. H. C. Bastian on Hetero genetic [Mar. 21, 



many of the spherical Amoebae were undergoing changes destined to result 

 in encystment. 



Fig. 3. — Phases in the Life-history of Monads and 

 Jmoebce. (x!670.) 



a-d. Representing the stages by which Monads became converted into Amoebae. 

 e-h. Stages by which such Amoebae became encysted. 

 i-m. Stages by which other Amoebae became resolved into Bacteria. 



On the tenth day, similar though more advanced changes were seen. Al- 

 though the majority of the Amcebse were still active and polymorphic, hun- 

 dreds of them were becoming encysted, and the different stages of the process 

 were quite obvious. They were these : — The previously spherical Amoebae 

 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 distance 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 diminished, and assumed a faintly brownish tinge. From the sur- 

 face of the developing cyst there were a number of very short ray-like pro- 

 jections (fig. 3, g). In the last stage, whilst the cyst-wall became more 

 developed and the projections more obvious, the whole exterior envelope 

 assumed a decidedly brown colour, and the contained protoplasmic mass, 



