10 PROTOZOOLOGY 



the soil is not yet clear in spite of the numerous experiments and 

 observations. All soil investigators should be acquainted with the 

 biology and taxonomy of free-living Protozoa. 



It is a matter of common knowledge that the silkworm and the 

 honey bee suffer from microsporidian infections (p. 670). Sericulture 

 in south-western Europe suffered great damages in the middle of 

 the nineteenth century because of the "pebrine" disease, caused by 

 the microsporidian, Nosema bombycis. During the first decade of 

 the present century, another microsporidian, Nosema apis, was 

 found to infect a large number of honey bees. Methods of control 

 have been developed and put into practice so that these micro- 

 sporidian infections are at present not serious, even though they still 

 occur. On the other hand, other Microsporidia are now known to in- 

 fect certain insects, such as mosquitoes and lepidopterous pests, 

 which, when heavily infected, die sooner or later. Methods of de- 

 struction of these insects by means of chemicals are more and more 

 used, but attention should also be given to biological control of them 

 by means of Protozoa and Protophyta. 



While the majority of Protozoa lack permanent skeletal structures 

 and their fossil forms are little known, there are at least two large 

 groups in the Sarcodina which possess conspicuous shells and which 

 are found as fossils. They are Foraminifera and Radiolaria. From 

 early palaeozoic era down to the present day, the carbonate of 

 lime which makes up the skeletons of numerous Foraminifera has 

 been left embedded in various rock strata. Although there is no dis- 

 tinctive foraminiferan fauna characteristic of a given geologic pe- 

 riod, there are certain peculiarities of fossil Foraminifera which dis- 

 tinguish one formation from the other. From this fact one can un- 

 derstand that knowledge of foraminiferous rocks is highly useful in 

 checking up logs in well drilling. The skeletons of the Radiolaria are 

 the main constituent of the ooze of littoral and deep-sea regions. 

 They have been found abundantly in siliceous rocks of the palaeozoic 

 and the mesozoic eras, and are also identified with the clays and 

 other formations of the miocene period. Thus knowledge of these two 

 orders of Sarcodina, at least, is essential for the student of geology 

 and paleontology. 



The history of protozoology 



Aside from a comparatively small number of large forms, Protozoa 

 are unobservable with the naked eye, so that one can easily under- 

 stand why they were unknown prior to the invention of the micro- 

 scope. Antony van Leeuwenhoek (1632-1723) is commonly recog- 



