PHYLUM PROTOZOA 



53 



increase in the number of chambers there is a multiplication of 

 the nucleus (Fig. 35, 4, b, nu). 



Not only does the shell increase in size by the formation of new 



g.Planorbulina 



Fig. 36, — Shells of Foratninifera. In 3, U, and 5, a shows the surface view, and 6 a section ; 

 8a is a diagram of a coiled cell without supplemental skeleton ; 5& of a similar form 

 with supplemental skeleton (s. sk.) ; and 10 of a form with overlapping whorls ; in 11a half 

 the shell is shown in horizontal section ; 6 is a vertical section ; a. aperture of shell ; 1 — 15, 

 successive chambers, 1 being always the oldest or initial chamber. (After Carpenter, Brady, 

 and BUtschli.) 



chambers : individual chambers become larger. In this process 

 layers of calcareous matter are added to the shell from without by 

 the agency of a thin layer of protoplasm that extends over the 



