62 Muscles of the sheath of Penis 



whether these muscles belong to the continuation of the seminal duct — which would be 

 quite different from what occurs in the two other sub-orders — or to penis itself. To decide 

 this point would have required a more abundant material for dissection than we had at 

 our disposal, as penis is rather thick. 



In all Opiliones penis is surrounded by a single chitinous sheath which for the greater 

 part is very thin. De Graaf has already pointed out the existence in Phalangioidre of 

 a couple of longitudinal strips which are thicker than the rest of the sheath; these strips 

 are also found and are much stronger in Ischyropsalis and particularly in Neviastoma lugubre, 

 but we have not found any such in Troguloid.se. It would follow that the strength of these 

 strips of chitine stands in a certain correlation to the thickness of the chitine in corpus 

 penis ; their function is probably, by means of theii- elasticity, to stretch the sheath both 

 when retracted, and, particularly, when exserted. Such strips of thicker chitine are not found 

 either in Laniatores or in Cyphophthalmi. 



The muscular equipment of the sheath is different in the three sub-orders of Opiliones 

 and likewise in the different families of Palpatores. Amongst Laniatores we have found it 

 similar in representatives of Gonyleptoidse, Assamioidse and Trisenonychoidse — three families 

 which are by no means nearly allied to each other. The sheath is here surrounded by 

 three layers of muscles. The direction of the fibres of the two innermost layers, which 

 are the heaviest, is oblique, in one layer to the right, in the other to the left, so that 

 the fibres cross each other (PI. VI., fig. 28, ?«(/). Posteriorly these muscles are inserted 

 on the collar-like expanded posterior extremity of penis, anterioi-ly they attach themselves 

 to the sheath somewhat behind the genital orifice ; there can consequently be no doubt 

 of the function of these two layers being that of facilitating the exsertion of penis. A third 

 moderately thin (in Acumontia) or very thin layer which Scirensen overlooked euveloi» the 

 other two ; its fibres are longitudinal on the lower surface, on the sides and above they 

 arc posteriorly essentially longitudinal, but towards the anterior end they are gradually 

 more and more transverse across the sheath ; with one end the fibres attach themselves 

 to the sheath posteriorly and along its dorsal side, with the other end they are fixed as 

 two oblong bundles beneath the sheath to the sternite, somewhat or only a little behind 

 the genital orifice. To judge from its attachments this muscular stratum must be capable 

 of contributing both to the exsertion and to the retraction of penis, in the first stages of 

 these acts. Muscles for the expansion of the sheath are not found in Laniatores ; but 

 operculum genitale (o) is furnished with one pair of muscles (PL VI., fig. 28, mo) which 

 serve to close it, and particularly to keep it closed when the animal desires to utilize for 

 other purpo.ses the pressure exercised on the interior organs by contraction of the segmental 

 muscles of abdomen. As in all other Opiliones a pair of niusculi retractores (??»') start from 

 the posterior extremit}' of penis and pass to the dermoskeleton at a point not far in front 

 of anus. 



In all the families of Palpatores the following three sets of muscles are found, viz. 

 one pair of m. retractores (PI. VI., fig. 22, vir), a pair of m. protractores (ibid, nip), both 

 of which have been noticed by earlier writeis, and a thii-d pair which has hitherto been 

 overlooked. As de Graaf has already pointed out in Phalangioidie, m. protractores rise 

 from the posterior end of the sheath, pass forwards and a little outwards, and fix them- 

 selves to the ventral dermoskeleton outside the sheath and a little in front of its middle. 



