27 
The President' s Address. By A. D. Michael. 
Hypopal stage before referred to occurs. A short history of the 
investigations into the nature of this stage u not a bad illustration of 
the gradual progress of knowledge of the Acarina. In 1735 de Geer 
noticed on the house-fly a tiny red mite with an oval body, having a 
polished chitinous carapace, and having instead of an ordinary mouth 
a minute tube apparently closed at the end but furnished with two 
sefce. The two front pairs of legs were well developed, but the fourth 
pair ended in setae instead of claws or suckers, in this resembling the 
Itch-Mites. It was taken as a species, and Linnaeus called it Acarus 
muscarum. Other writers added new allied species, until it came to 
Dugks, who in 1831 created the genus Hypopus for them. Other 
writers continued to add species, and Koch in 1818 divided the genus, 
forming a new one, Homopus , to receive some of the creatures. Gervais 
next added a new species, which oddly enough he associated with 
Tyroglyphus, although apparently without any idea of the connection 
which has lately been ascertained to exist between them. Up to 1847 
no one doubted that these were adult creatures forming a separate 
group of Acari, but at this time Dujardin made a great advance; he 
expressed his opinion that they were all immature forms ; he called 
attention to the numerous ventral suckers by which they attached 
themselves to other creatures, and to the absence, as he considered, of 
any mouth-organs and of any reproductive organs. He observed that 
certain Hypopi immediately before ecdysis contained within their skin, 
and completely filling it, an Acarus very different from themselves and 
possessed of chelate mandibles and palpi ; he found them associated with 
Gamasids larger than themselves ; Gamasids had chelate mandibles 
and palpi ; the deduction was obvious, and Dujardin announced that 
Hypopus was an immature form of Gamasus. In 1861 Furstenberg 
found a number of Hypopi on the skin of a stuffed elephant ; he re- 
verted to the old idea of their being special adult creatures ; with his 
accustomed minuteness he described their maxillae and the number of 
joints in their palpi ; he carried his measurements to the 1/10,000 of a 
millimetre. The only unfortunate part is that as these creatures do 
not possess maxillae or palpi there has been a little difficulty in under- 
standing what Furstenberg meant. Next Gerlach tried the subject ; 
he had been studying the Itch-Mites; the hind legs of Hypopus 
resembled those of Itch-Mites, and had not Furstenberg found them 
on the elephant? It was not at all surprising that Gerlach should 
proclaim them to be Itch-Mites. In 1868 Claparede brought his 
genius and industry to bear upon the subject. He had been studying 
the life-history of Hoplophora, one of the Oribatidae, which is soft and 
white when immature, but hard and brown when adult. Claparede 
found a new species of Tyroglyphus, he kept it in confinement, 
breeding large numbers over a period of three years, but he never 
could detect a male ; he did not find any Gamasids amongst them, 
but he did find numbers of Hypopi, and he actually saw nymphs of 
the Tyroglyphus , which greatly resemble the adult, cast the skin and 
