PROTOZOA AND DISEASE. 



117 



hints in the Silurian and Devonian ; and an abundant representation in 

 rocks of the Carboniferous and several subsequent epochs. The shells 

 of calcareous Foraminifera form an important part of chalk deposits. 

 The famous Eozoon canadense of Cambrian rocks is regarded by most 

 as a purely mineral formation. 



There seem at least to be sufficient relics to warrant Neumayr's 

 generalisation in regard to Foraminifera, that the earliest had shells 

 of irregularly agglutinated particles (Astrorhizidce), that these were 

 succeeded by forms with regularly agglutinated shells, exhibiting types 

 of architecture which were subsequently expressed in lime. 



Relics of siliceous Radiolarian shells are also known from Silurian 

 strata onwards, with, perhaps, the exception of the Devonian. Best 

 known are those which form the later Tertiary deposits of Barbados 

 earth, from which Ehrenberg described no fewer than two hundred and 

 seventy-eight species. 



and Disease. --The discoveries of recent 

 shown that the study of Protozoa is* an 



Protozoa 



years have 



inquiry of growing practical interest and importance. 

 This is particularly so in regard to diseases both in 

 man and in his stock. Upwards of thirty Protozoa 



FIG. 51. Glossina palpalis, tse-tse rly. 



representing the main divisions of the group are known 

 at some stage of their life history to be parasitic in the 

 human body, and some of these are associated with 

 serious and fatal diseases. Am&ba coll is related to an 



