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In I842 the Frenchman Berger discovered the mite Demodex folliculorum and later introduced this parasite to medical science (Berger, I845). After more than a century of sporadic literature on this topic, there has been a resurgence of interest in ophthalmology triggered off by a stimulating thesis on Demodex folliculorum blepharitis (Coston, i967).Belonging to Class Arachnida, Order Acarina, Demodex folliculorum can infest the eyelashes, hair, and meibomian and sebaceous glands of man. The adult (Fig. I) is vermiform in appearance, measuring 280 jl in length in the male, 270 to 440 i in the female, and can be found in great numbers in the hair follicles. Possessing a well-developed prostoma and biting apparatus, the octopod Demodex folliculorum is characterized by distinctive annular markings on the abdomen. The legs, though rudimentary, are quite active and when placed on a microscope slide the parasite demonstrates an impressive degree of mobility.The clinician can readily demonstrate this property in vivo by causing evacuation of the hair follicle when the skin surface is stimulated with an irritating agent such as ether. Even so, in the presence of the bright light of the biomicroscope, complete evacuation does not occur, as the head appears photosensitive, and the observer becomes aware of its presence only by the sight of a number of cream-coloured tails protruding from the lid margin like fine bristles. F I. GI Adult Demodex folhculorum located on an eyelash. X 425

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(rats). Taxonomic characteristics including the nature of the dorsal spines on the capitulum, the proportions of the body, location of the male genitalia and the shape of eggs are invaluable pointers in differentiating these species. Some of these mites display systemic involvement of the lymphatics and blood stream but this feature has not been observed in man.Two congeric species of Demodectic mites occur in the eyelid of man. The more common and longer vermiform-shaped parasite Demodex folliculorum is found in the eyelash and hair follicles, whilst Demodex brevis is located in the meibomian glands AbstractIt is well established that Demodectic mites can infest the meibomian glands, eyelash and hair follicles of the eyelid. In this study, scanning electron microscopy revealed Dernodex folliculorurn occurring freely on the skin surface of the eyelid. This indicates some mobility and implies further vector potential. Exoskeletons from these parasites also occur on the eyelid. Key words: Eyelid, Dernodex FolliculorumDemodectic mites constitute the most common ectoparasites found in man and occur mainly in the facial,' m a m m a r~,~ axillary' and pubic region. 'Other species of Demodectic mites have numerous hosts throughout the animal kingdom and include D. cunis, which causes common mange