POLYSTOMELLA. 



93 



shell or are liberated by the protoplasm creeping out and 

 forming a halo of anastomosing threads round the deserted 

 test. The spores secrete 

 a shell and grow into the 

 typical megalospheric forms. 

 When the megalospheric 

 form is about to reproduce, 

 its nucleus disintegrates and 

 is replaced by numerous 

 scattered nuclei formed 

 around chromidia. The 4 

 protoplasm segregates into 

 little masses, each centred 

 in a nucleus. Each of 

 these nuclei divides by 

 mitosis into two, then into 

 four, and the division of 



the nucleus is followed 

 by the division of the 

 protoplasmic mass, so that 



FlG. yf.Polystomella, megalo- 

 spheric form, with large central 

 chamber (M) and one nucleus 

 (N). After Lister. 



hosts of tiny cells are 

 formed. These become provided with flagella, swim out 



FIG. $>.PolystomeUa, microspheric form, with small 

 central chamber (c.c. ), numerous nuclei (N)> bridges of 

 protoplasm between chambers (B), After Lister. 



