30 Life Historjj and Eco}ioiny of the Cheese Mites 



were made by fixing a glass ring about one-eighth of an inch in height 

 to a slide. The adult male and female were then placed in the cell 

 along with a small piece of cheese, the base of tlie cell having been 

 previously covered with a piece of blotting paper, which was kept 

 moist. The upper rim of the glass circle was smeared with vaseline 

 and a small strip of glass placed on the top as a lid to prevent the 

 mites escaping. The cells were examined every day under the micro- 

 scope and reco]"ds of the duration of the various stages were kept. 

 When about three eggs had been laid the male and female were removed 

 but the eggs left. The exact date when the egg was laid was therefore 

 known and the young stages became used to living in the cell. It 

 was much more difficult to keep the mites alive, if the cells were 

 started with the larva or the nymph stage. 



The eggs are white oval bodies, so small as to be only just visible 

 to the naked eye. They hatch in about 10 — 12 days after being laid. 

 On hatching, the young mite is known as a larva. It is colourless 

 and of a glassy appearance, and has three pairs of legs only. The 

 larva feeds actively for about a week, then becomes c[uiescent and 

 casts its skin, emerging as t\\e first yiymjih. The first nymph has four 

 pairs of legs and is somewhat larger than the larva. It moults again 

 and becomes the second nymph, larger and more highly ciiitinised than 

 the first nymph. After its third moult, the mite emerges as an adult 

 male or female, the sexual organs not being functional until the final 

 stage is reached. 



In Tyrogly pints longior, however, there is an additional stage after 

 the first nymph stage, which is specially adapted for distributing the 

 species. This stage is known as the Hypopus stage and occurs under 

 favourable conditions, that is, when the mites are allowed to breed 

 unchecked. The Hypopus is like a minute tortoise. It is extremely 

 small, pinkish in colour, and has a hard, shelly back of chitin. The 

 legs are short, the mouth parts rudimentary, and there is no evidence 

 that it feeds. On its ventral side it has a sucker plate by means of 

 which it attaches itself to other mites, to flies and moths which alight 

 on the cheeses, or even to the skin and clothes of human beings. It 

 is thus cai-i'ied about until it finds a suitable place, when it drops off, 

 moults to become a second nymph, and commences feeding.' 



Practical Considerations. 



The following questions present themselves foi' solution . 

 (1) How do new dairies become infected with mites? 



