Protozoa. 19 



of house-building but have no nuclei, and are thus the 

 simplest conceivable living beings, mere specks of 

 living jelly (fig. 9). Of these naked forms, some authors 

 make a separate class under the name Monera. 



Class 1. Rhizopoda. In the fine white sand on 

 the sea-shore or in the mud of the sea-bottom there are 

 to be found minute calcareous shells of varying forms, 

 ranging from -yj-g-th to -j^th of an inch in diameter. 

 Each shell consists of many separate chambers, 

 arranged either one after another in a straight line 

 or in a single or double spiral, or even grouped in 

 more complex fashions. Each chamber is separated 

 from its neighbours by a partition which is pierced 

 with one or many holes whereby the several chambers 

 communicate with each other. The shell-substance 

 is either white and porcelain-like, or glass-like and 

 more brittle, and pierced not only in the partitions but 

 over its whole surface by numerous holes. On ac- 

 count of these perforations these little shells are called 

 Eoraminifera (hole bearing). 



The animals which build these wonderful houses 

 are exceedingly simple in their structure. The interior 

 of each chamber in a fresh state is filled with proto- 

 plasm which is jelly-like, highly contractile on being 

 irritated, and not only extends through the holes in 

 the shelly wall but coats the outside of the shell with 

 a glairy external living layer. This layer has no defi- 

 nite uniformity of outline, but is constantly changing 

 its shape by sending into the surrounding water 

 radiating protoplasmic processes which are incon- 

 stant, rapidly retracted, disappearing by being taken 

 into the homogeneous matter of the animal's body, 



C2 



