380 MR, A. D. MICHAEL ON HTPOPI, 



It remained to be seen whether I sliould be able to verify bis 

 conclusions as to tbe causes of the transformation. Por this pur- 

 pose I allowed tbe cell to get dry, but I did not thereby obtain 

 any increase in the number of Hypopi; although I did find a very 

 great diminution in the number of Tyroglyplii, which died off, as 

 the moisture became insufficient, until they disappeared altogether. 

 Upon redamping the cell more larvse and young nymphs soou 

 made their appearance from the eggs which the previous adults 

 had laid, and older nymphs from the Hypojoi were found under- 

 going ecdysis ; but this occurred gradually, not all at once : tbe 

 Hypopi did not vanish suddenly, nor were fresh adults to be 

 found until they had grown. It must be remem.bered that I did 

 not introduce fresh fungus into my cells as Megnin did. 



This experiment of allowing the cells to dry, or partially dry, 

 was repeated several times, but always, practically, with the 

 same results. It would seem, therefore, that desiccation or other 

 unfavourable circumstances, will not necessarily cause Tyroyly2'>hus 

 nymphs to change into IIyp)opi more rapidly than they would 

 otherwise have doue. 



In the spring of 1882 I resumed the subject. I was staying 

 at a farm-house where they had an old-fashioned chaff-house 

 adjoining the stable : this was not kept in the well-swept 

 condition usual in modern stables, but the chaff and debris of 

 the fodder were allowed to remain in a pile on the brick floor, 

 which was always rather damp, and altogether the conditions 

 were as favourable to Tyroylyphus life as can well be imagined — 

 warmth, moisture, and abundant food were there, and, conse- 

 quently, the chaff was teeming with life ; TyroglypM were swarm- 

 ing, Gramasids were there in quantities preying upon them, and 

 minute Diptera and their larvse, Myriapoda, &c., were abundant ; 

 but Hypopi also loere in great profusion, and continued to be so, 

 and to attach themselves to every living insect or Gamasid which 

 came into the chaff*. It was evident, therefore, that the most 

 favourable circumstances did not prevent the Tyroglyplms be- 

 coming a Sypopus. The principal species of Tyroglyplms were 

 T.farince, T. onycopJiagus, and Megnin's T. rostro-serratus (sub- 

 sequently called Serrator ampMhius by him, Phyllostoma pec- 

 tineiim by Kramer*, and Histiosfoma pectineum by Cauestrini 

 and Berleset)- 



* " Beitrage zur JSTaturgeschichte der Milben," Archiv fiir Naturgesch. xlii. 

 Jahrg. 1876, p. 39. 



t "NuotI acari," Atti Soc. Ven.-Treiit di Sci. nat., vol. viii. 1881. 



