340 THE MITES 



the body is hard and chitinous, there is no mouth or mouthparts, 

 the legs are short and stumpy, and there is usually a raised area 

 on the ventral surface with a number of tiny sucking discs. By 

 means of these suckers the hypopus attaches itself to insects or 

 other creatures and is thus transported to 

 new localities, the entire object of the 

 hypopus stage apparently being to secure 

 passage to new breeding grounds. After 

 dropping from its unwilling transporter 

 the hypopus moults into an eight-legged 

 nymph again, which, after feeding, develops 

 _ into an adult. 



/ The Tyroglyphidse are all quite similar 



FIG. 141. Hypopus or j n appearance, and the characters which 



traveling stage of Tyro- 



giyphus, ventral view, separate the species, and even the genera, 

 Much enlarged. (After are f ew an( j m i nu t e . A considerable num- 



Banks.) 



ber of species may attack persons who 

 handle infested materials, and they are the cause of " grocers' 

 itch." This affliction is caused especially by various species 

 of Glydphagus and Tyroglyphus. Of historical interest is a 

 case of dysentery apparently due to a Tyroglyphus, T. longior, 

 (Fig. 140) which occurred in one of Linnaeus' students. The 

 mites were abundant in his faeces, and were found to live and 

 multiply in a juniper-wood cup which he used. As shown by 

 Castellani, an itching rash known as " copra itch," occurring 

 among the laborers in the copra mills of Ceylon where cocoanut 

 is ground up for export, is caused by a variety of this mite, called 

 T. longior castellanii. Copra itch occurs also among stevedores 

 who handle copra in London. Another species, Glydphagus 

 buski, was taken from beneath the skin on the sole of the foot 

 of a negro in England; it had caused large sores. The negro 

 attributed the affliction to the wearing of a pair of shoes loaned 

 him by a similarly affected negro from Sierra Leone, Africa. 

 Another species, Rhizoglyphus parasiticus, which lives on roots, 

 bulbs, etc.j in India, produces a skin disease among coolies work- 

 ing on tea plantations. It begins with blisters between the toes 

 and spreads to the ankles, causing very sore feet. 



Other Species. A few species of the family Tetranychidae, 

 including the " red spiders " or spinning mites, occasionally 

 become troublesome to man, although they are normally vege- 



