40 Fresh- Water Mites. [Sess. 



into an attitude of defence by tucking in its body, bead and 

 feet, and converting itself into a ball of impervious prickles. 

 Protected by this hedge or fence, the hedgehog is one of the 

 most curious objects in nature. 



VII.— ^ FEW WORDS ON FBESH-WATEB MITES 

 {HYDRA CHNIDM). 



By Mr C. D. SOAR, F.R.M.S., Etc. 

 (Communicated, Feb. 25, 1903.) 



The study of these interesting creatures was commenced a 

 great number of years ago, the earliest known writer on them 

 being Stephan Blankaart, a Hollander, who published his 

 paper in Amsterdam in 1688. Then came Swammerdam, 

 Linn^, Eoesel, De Geer, and others ; but the first really seri- 

 ous attempt to study and name these very beautiful objects 

 was when 0. F. Miiller began to write about them in 1776. 

 In 1781 he published his great work on water-mites — 

 ' Hydrachnse quas in aquis Danise palustribus detexit de- 

 scripsit,' &c., 1781. Lipsiffi. The opening words of this 

 volume are particularly interesting : it shows the enthusiasm 

 of the man in his solitary hobby, and how he tried to induce 

 others to take it up, but without result. I think it may be 

 as well to give you some of his own words from his book : — 



" Twelve years have now passed since I laid before the public a genus 

 of insects full of unknown species, and mentioned their specific names in 

 Danish, German, and French, in order that I might excite in entomolo- 

 gists a stimulus for learning about this new genus. I called them Hy- 

 drachnas, or water-spiders, because they chiefly resemble spiders and land 

 acari, but they always live in water. They were close at hand, and they 

 deserved no slight consideration on account of the many varieties of their 

 form, the beauty of their colours, and the singular character of their 

 multiplications and copulations, and because they are not infrequently 

 swallowed by our cattle in drinking water. I added that they could be 

 sent anywhere in a bottle filled with water, and I promised that I would 

 repay all expenses and publicly offer my thanks to those who were de- 



