152 BRITISH TYIiOGLYPHID^. 



and became the principal authority upon it. He first 

 attacked it in his memoir upon Histiostoma rosfro- 

 serratum, called by him at that time Tyroglyphus roslro- 

 serratus* and afterwards in that upon Hypopus ;t his 

 labours were rewarded by the French Academie des 

 Sciences with the Thore prize of 1873. Megnin experi- 

 mented upon Histiostoma rostro-serratum and Tyro- 

 glyphus mycophagus, both species found by him in 

 immense quantities upon mushrooms (Agaricus cam- 

 pestris). He bred his creatures in large cases, supply- 

 ing them with pieces of fresh mushroom from time to 

 time; he saw the Hypopus inside the inert nymph of 

 Tyroglyphus just as Claparede had done ; he also found 

 that Hypopus turned into a nymph of Tyroglyphus. 

 Megnin also noticed that when the mushrooms and 

 cages got dry his Tyrocjlyplii disappeared and were 

 apparently replaced by swarms of Hypopi ; when 

 moisture, or fresh moist mushroom was added the 

 Hypopi disappeared and the TyrogJyphi were again in 

 great quantities. Specimens kept in separate cells 

 appeared to be almost inert, and adhered motionless to 

 the side of the cell; but when moisture was added 

 these Hypopi turned into nymphs of Tyroglyphus. The 

 construction which Megnin put upon these facts was 

 the very natural one that Hypopus was a form into 

 which the nymphs of Tyroglyphus changed when, 

 through dryness of the atmosphere or other causes, 

 there was a difficulty in their continuing to live as 

 Tyroglyphi, and that it was a provision of nature to 

 insure the preservation of the species by carrying it 

 over periods of drought, etc. Megnin declared that 

 Fiirstenberg's mouth-organs of Hypopi were pure fancy, 

 and condemned such exercises of imagination. He 

 judged correctly that Hypopus, Homopus, and Tricho- 

 dactylus were all forms of similar nature, and he 

 asserted that they had the power of living without any 



* " Memoire anatomique et zoologique sur nn nouvel Acarien, etc.," 

 in ' J. Anat. Physiol.' (1873), t. ix, pp. 369378, pis. x xii. 



f " Meinoire sur les Hypopus, etc.," ibid. (1874), t. x, pp. 225254. 



