198 MITES AND TICKS 



Ixodes reduvius is water-proofed by an external covering of wax 

 which is secreted by the female after the shell layers are complete. 

 This waxy covering is first smeared over the egg as it passes down 

 the vagina and a further layer of lipoid is applied when the egg 

 touches Gene's organ, a glandular structure that is everted shortly 

 before oviposition. In Ornithodorus moubata the wax is applied 

 solely by Gene's organ: this difference may be related to the size 

 of the egg which is relatively small in the Ixodoidea. The wax is 

 probably secreted through pore canals distributed over a narrow 

 zone of cuticle between the horns of the organ, and the cement 

 covering layer of the epicuticle does not extend to this zone. 



Sexual dimorphism is rare in Thrombidiform mites although it 

 does occur in some genera of water mites, sometimes even affect- 

 ing the nymphs. It is also to be found in the Tarsonemini and in 

 the genus Temiipalpus of the Tetranychidae and some few others. 

 It is therefore of interest that Turk and Phillips (1946) found 

 rudimentary sexual dimorphism in the slug mite Riccardoella 

 limacum (family Ereynetidae), a species in which the adult stage is 

 disappearing. The female deutonymph produces the eggs which 

 are capable of fertilisation, but whether the larger adult female also 

 lays eggs is undecided. The eggs mature in their own oocysts and 

 some at least are fertilised in the ovary. Copulation takes place on 

 the host and is probably confined to the early summer, the only 

 time at which adult males are found. The eggs are commonly laid in 

 the mantle cavity of the host, but may sometimes be found em- 

 bedded in mucus on the skin. Viviparity and oviparity exist side by 

 side and seemingly not all individuals retain an egg of retarded 

 development over the winter, while some over-wintering larvae 

 remain in the dry skin of the female. 



In the Bdellidae the sexes are very similar. The eggs are slightly 

 elliptical and are covered with clavate spines and projections. They 

 are laid on the soil, in leaf mould or wherever the mite happens to 

 be and hatch into a typical six-legged larva which develops through 

 three nymphal stages to the adult. 



The life cycles of the red-spider mites are comparatively well 

 known. The winter is passed as eggs which are deposited on 

 branches and twigs and are bright red in colour. They hatch in 

 spring to a larva which passes through various nymphal stages to 



