When studying the fauna of the soil it is obviously of the utmost importance to use such methods of collecting the animals as are thoroughly reliable and efficient, so that one can be reasonably sure of getting practically all the animals existing in a given material. It is not to be expected that one method will ensure successful collection of all the animals, because some react in one way towards the agents chiefly used, viz., strong light and heat, others react in another way. For instance, some animals, such as Tardigrades and Rhizopoda, encyst themselves when subjected to dryness and cannot be forced to move downwards away from the light and dryness as most arthropods do. As pointed out by the author (1928) all methods of mechanically separating the animals from the substratum by sieves, etc., are worthless unless applied to larger animals such as Oligochaeta, larger beetles and snails. For all smaller animals the only safe method is the automatic one based on their reactions towards light and dryness, which was devised by the late Professor A. Berlese in Florence in 1905.
This apparatus is so well known that it is not necessary to give a detailed description of it, nor need I dwell on the more or less similar apparatus constructed later, except Tullgren's, because the latter, constructed in 1917, has been used by several investigators. Tullgren substituted the funnel filled with water and heated by gas, which Berlese used for the purpose of drying the material containing the micro-arthropods to be collected, by an electric bulb suspended above the material in a cylindrical funnel at a distance of about 5 cm. above the material.
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