DEVELOPMENT AND IMMATURE STAGES. 157 



emerges after the ecdysis, leaves behind it the cast 

 skin of the ordinary nymph, quite clean, like any other 

 cast skin, and without any torn particles of internal 

 organs adhering to it. Sixthly, the Hypopus has not 

 any mouth-organs except the external lip which closes 

 the mouth-opening, or rudimentary mouth-opening, and 

 therefore apparently has not any means of destroying 

 its host. Seventhly, the Hypopus returns to the Tyro- 

 glyphus -nymph form after the ecdysis. This last reason 

 would be sufficient alone. 



If the above reasons dispose of Andrew Murray's 

 view, as I think they do, they equally dispose of the 

 idea that Hypopus is a separate adult creature ; for 

 that could now only be sustained if Murray's view were 

 accepted, otherwise the evidence of Claparede, Megnin, 

 Berlese, Macintyre, and myself, and later on of Monier, 

 would doubtless be considered sufficient to prove that 

 Hypopus is a stage in a life -history. 



Claparede's view that Hypopus is the adult male of 

 Tyrog typhus, or rather had he known it of Rhizoglyphus, 

 was as above stated practically disproved by Claparede 

 himself, and by Fumouze and Robin. It will, I think, 

 be found that it was even more effectually disproved 

 by my own investigations in 1882, mentioned below, 

 which also answered Gervais' idea ; there only re- 

 mained Megnin's and Haller's explanations. My 

 observations decidedly confirmed Megnin's view, so far 

 as it stated that Hypopus is a heteromorphous nymphal 

 form of Tyroglyphus and some allied genera. It 

 remained to be seen whether I could confirm his con- 

 clusions as to the cause of the transformation. 



For the last-named purpose I allowed my cells with 

 Tyroglyphus nymphs to get dry, but I did not obtain 

 any increase in the number of Hypopi ; although I did 

 find a very great diminution in the number of Tyro- 

 glyphi, which died off as the moisture became insuffi- 

 cient, until they disappeared entirely. Upon redamping 

 the cell, but without introducing any fresh material or 

 allowing any communication with the exterior except 



