156 BRITISH TYROGLYPHID^. 



For two or three years I carefully watched Tyro- 

 glyphi in confinement in small glass cages under 

 favourable and unfavourable conditions ; but my efforts 

 were chiefly directed to Tyroglyphus siro and T. longior, 

 and I did not succeed in getting any hypopial forms 

 from them, nor in seeing anything that would elucidate 

 the question. I have lately succeeded in breeding the 

 hypopial nymph of T. longior, which will be figured in 

 this book in its proper place, but it is very difficult to 

 obtain. In 1881, however, I found a quantity of 

 Megnin's Tyroglyphus mt/cophagus. I soon found that 

 with this species there was not any difficulty in obtain- 

 ing and rearing the Hypopus, or in repeating Megnin's 

 experiments. The nymphs readily turned into Hypopi, 

 and the Hypopi returned to the condition of nymphs 

 of the Tyroglyphus ; in each case by an ecdysis. I was 

 able to procure and retain microscopical preparations 

 made during the progress of the change, and showing 

 the Hypopus forming or formed inside the Tyroglyphus 

 nymph. This appeared to me a sufficient answer to 

 Andrew Murray's view that Hypopus was an internal 

 parasite ; because, firstly, the Hypopus is very nearly 

 as large as the Tyroglijphus from which it emerges, 

 filling up the whole interior ; which seemed highly im- 

 probable in a creature which cannot grow inside, for 

 no one has ever seen a young Hypopus either within 

 the Tyroglyphus or living free ; all Hypopi of the same 

 species being about the same size and obviously in the 

 same stage of growth. Secondly, a Hypopus is not 

 ever seen within a larva or within an imago, only 

 within the nymph ; although all three stages in Tyro- 

 glyphus are soft-bodied and very similar. Thirdly, we 

 never see two Hypopi within the same nymph, although 

 when the Hypopus has emerged many specimens, some- 

 times immense numbers, may be found, ecto-parasitic 

 upon the same Gamasid or insect. Fourthly, the 

 emerging of the Hypopus is preceded by an inert 

 period, just as the ordinary ecdysis is in most Acarina, 

 including Tyroglyphus. Fifthly, the Hypopus, when it 



