An Egg-waxing Organ in Ticks
Authors: Lees A. D. , Beament J. W. L. 
Published: April 2021

1. During the oviposition of ticks a glandular organ—the organ of Gêné— is everted and touches the egg. If it is prevented from everting most of the eggs shrivel rapidly; few hatch even in a humid atmosphere.

2. The waterproofing properties of the normal egg are conferred by a superficial coating of wax, 0 · 5 – 2 ·0 μ in thickness. In Ornithodorusmoubata the wax is secreted and applied solely by Géné’s organ. In Ixodes ricinus waterproofing takes place in two stages: an incomplete covering of wax, probably secreted by the lobed accessory glands, is first smeared over the egg during its passage down the vagina; waterproofing is then completed by a further application of wax from Géné’s organ after the egg has been laid. Owing to its superficial position on the egg the wax layer is readily attacked by solvents and emulsifiers.

3. The morphology of Géné’s organ in O. moubata is described. The gland is a proliferation of the epidermis which lies detached from the cuticle. Its secretion, a watery refractile liquid containing the wax precursor, accumulates between the gland and the cuticle in two horn-like extensions. The wax is probably secreted through pore canals distributed over a narrow zone of cuticle below the horns; the cement covering-layer of the epicuticle does not extend to this zone.

4. The transparent, heat-stable material isolated from the horns of Géné’s organ is regarded as the wax precursor. Solubility in water is probably conferred by chemical linkage with protein. The precursor is taken up from the horns, where it is stored, and is presumably broken down within the gland cells. The wax is then secreted through the pore canals while the protein moiety is retained by the cell.

5. The critical temperatures of the eggs of Ixodidae range from 35° C. in I. ricinus to 44° C. in Hyalomma savignyi; only slightly higher critical temperatures were recorded for Argasidae (45° C. in O. moubata). Eggs with lower critical temperatures are more susceptible to desiccation. The susceptibility of the eggs of a given species is of the same order as that of the parent species; but whereas in Ixodidae the critical temperatures of the egg and the cuticle of the female tick are approximately the same, in Argasidae the critical temperatures of the cuticle are much higher (62° C. in O. moubata). These differences are related to the physical properties of the waxes. The cuticular wax in O. moubata is hard and crystalline (m.p. 65° C.), whereas the egg wax is soft and viscous (m.p. 50-54° C.).

6. The natural wax from Géné’s organ has definite powers of spreading on the surface of the egg and so completing the waterproofing layer.

7. The material extracted with boiling chloroform from egg-shells or from nymphal cuticles separates spontaneously into two fractions, a hard white wax (c. 85 per cent, by weight) and a soft yellow grease (c. 15 per cent.). The properties of these two lipoids differ conspicuously from those of the natural wax. Attempts to deposit the extracted materials on membranes in the form of a waterproofing layer were unsuccessful.

8. Ovulation is described in O. moubata. The shell of the tick egg is secreted by the oocyte itself and not by follicle cells. Three layers can be distinguished in the 24-hour egg: (i) an outer wax layer; (ii) an incomplete layer of granules which reduce ammoniacal silver nitrate; (iii) a shell layer. A fourth layer, the inner membrane (iv), is secreted by the oocyte after incubation for 2-3 days.

9. Both the shell layer and the inner membrane are composed of resistant, elastic protein and are devoid of chitin. The shell layer of the unwaterproofed egg is highly permeable to water and to large molecules with either hydrophilic or lipophilic affinities. The inner membrane is at first freely permeable to water and to inorganic ions. During the course of incubation the wax gradually migrates into the shell material and may reach the inner membrane. As this occurs, the effectiveness of abrasive dusts and of chloroform in promoting increased transpiration through the shell is notably reduced.