Miiscles of the sheatli of Ovipositor 57 



assumed to be the rule in Palpatores. In Laniatores and Cyphophthalmi, on the contrary, 

 ovipositor has only one single sheath. In Cyphophthalmi the sheath is thin' in the greater 

 part of its length, but fairly rigid, so that it does not collapse after being cut open, even 

 if ovipositor is taken out of it. In Laniatores (PI. VI., fig. 8) the sheath is to a con- 

 siderable extent covered by a muscular stratum {ins) of which the posterior extremity, as 

 in all Opiliones, is fixed to that place where the sheath joins the base of ovipositor; from 

 this place the muscular fibres pass first forwards, but somewhat to the side, then making 

 a rather sharp bend backwards and a little outwards, in order to attach themselves to 

 the inside of the sternite, a little more laterally off the base of ovipositor. In Tricenonyx 

 we found this structure a little deviating : only a portion of the fibres of the muscular 

 stratum turns backwards from the lateral part of the sheath, while other fibres proceed 

 farther forward on the sheath itself and terminate there. There are besides here a pair 

 of muscles {mo in PI. VI., fig. 8), which attach themselves to the posterior angle of 

 operculum genitale and clearly serve to close it and to keep it closed. The function of 

 this pair of muscles is not principally to close operculum genitale, but to keep it closed, 

 when the animal contracts its segmental muscles for any other purpose than to push out 

 ovipositor or penis, because the same holds good for both organs. When the segmental 

 muscles are in action a pressure is of course exercised on the whole interinr of the animal, 

 with all the organs which are found there. What the effect of this pressure will be, 

 depends in each case on which other muscles at the same time contract or not ; because 

 if the muscles serving for the evacuation of an}' organ act at the same time, the evacuation 

 of the contents takes place so much the more quickly ; but if the sphincter of the organ acts, 

 the contents are kept back. We may here mention a direct observation made by Sorensen 

 {h, p. 182) with regard to Laniatores to the effect that it is possible by means of a gentle 

 pressure on that part of abdomen which consists of separate segments, to cause the liquid 

 to flow out from the odoriferous glands and generally also from the urinary bladders^, and 

 that, he sa3's, "all the more easily, when the animal has been killed and the sphincters 

 consequently act only vi inertke. The liquid is almost always evacuated, in greater or 

 smaller quantity, when the point of the knife is pressed against the skin in order to cut 

 open the body, the skin being, as will be remembered, very tough and not at once penetrated 

 by the knife ; it is so far indifferent where the knife presses the skin." In another place 

 Sorensen says {ihid. p. 203): "When the point of the scalpel is introduced where the ventral 

 surface of abdomen joins the inner border of the last pair of coxa>, penis is often 

 suddenly exserted — particularly when at the same time operculum genitale is opened with 

 the point of a needle — and as a rule, not only the whole of penis but with it a portion, 

 about one half, of the sheath is exserted before the knife breaks the skin." But the exsertion 

 of penis or ovipositor with the appertaining sheath must, on account of the rather large bulk 

 of these organs, diminish the pressure exercised on abdomen. It is therefore clear that the 

 muscles which close operculum genitale offer the animal a powerful means of emptying the 

 other organs. The mechanical principle whicli operates here is evidently the same as we 

 see in mammalia, where the pressure produced by the action of the expiratory muscles 

 on the interior of the thoracic cavity and — indirectly — of the body in general, when epiglottis 

 is closed, is utilized to facilitate the evacuation of urine and excrements. 



' In Ptireellia the sheath is more firmly chitinized at its anything similar occurs in the other genera, 

 junction with the outer skin in the genital aperture, forming - Neither the urinary bladders nor the odoriferous glands 



there an obversely hastate plate. We do not know whether are provided with any muscular stratum. 



s. S 



