Introduction 33 



Reproductive System: The Acarina are all dioecious. In most groups 

 the males can be distinguished from the females even though males 

 and females are similar to each other. Fertilization is internal, but the 

 methods by which the spermatophores are introduced into the female 

 reproductive system vary considerably. Some mites develop young 

 parthenogenetically but none has been shown to be exclusively parthe- 

 nogenetic. Mites may be oviparous or ovoviviparous. Only sexual repro- 

 duction is known. 



The male reproductive system consists of a testis or pair of testes, 

 vasa deferentia, accessory gland or glands, an ejaculatory duct, and a 

 penis. The penis is lacking in the Mesostigmata where the spermato- 

 phores are introduced into the female by the chelicerae. Many males 

 have one or more pairs of legs modified as organs for grasping the 

 female during copulation. 



The female reproductive system consists of an ovary or pair of 

 ovaries, an oviduct, uterus, seminal receptacle, accessory glands, and 

 in some cases a vagina. There is a specialized ovipositor in some 

 groups (Oribatei), but usually the eggs are laid through the genital 

 opening without the aid of an ovipositor. 



The genital openings of both males and females are usually closed 

 by specialized plates that frequently have genital suckers associated 

 with them or near them. In most mites examination of the genital 

 opening is sufficient to distinguish the sexes but in some the presence 

 or absence of a penis is the only reHable criterion, while in others 

 examination of the gonads is required. 



The spermatozoa are frequently immature when transferred to the 

 female and mature only after copulation is completed. Most mites 

 develop one or a few eggs at any time but the ticks and some of the 

 tarsonemids develop numerous eggs concurrently. 



Most eggs are provided with an eggshell that protects the developing 

 embryo. In some cases eggs can be transported by wind currents for 

 great distances. 



Life Cycle: The primitive life cycle consists of an egg in which the 

 blastula develops, a deutovum formed by a chorion that is secreted by 

 the blastoderm, a six-legged larva, a protonymph, deutonymph, trito- 

 nymph, and adult males and females. So many families deviate from 

 this primitive life cycle, however, that it is the exception rather than 

 the rule. The life cycle of many of the mites is still to be determined. 

 In most mites the larvae, except for the absence of the genital open- 



