CHAP. XIV The Simplest Animals 221 



showed that Infusoria were single cells comparable to those which 

 make up a higher animal. For the resemblance between some of 

 the spirally twisted shells of Foraminifera and those of the 

 immensely larger Molluscan Ammonites and Nautili led many to 

 maintain that the Foraminifera were minute predecessors or else 

 dwindling dwarfs of the Ammonites. So Ehrenberg (1838) figured 

 the presence of many organs within the Infusorian cell. But as 

 the microscope was perfected naturalists were soon convinced that 

 the Protozoa were unit masses of living matter. This is their great 

 interest to us ; they are, as it were, higher organisms analysed into 

 their component elements. We see them passing through cycles 

 of phases, from ciliated to amoeboid, from amoeboid to encysted, 

 cycles which shed light upon changes both of health and of disease 

 in higher animals. Again, they seem like ova and spermatozoa 

 which have never got on any farther. 



