COMPARATIVE MORPHOLOCxT OF THE GALEODID^. 333 



In the Pseiuloscorpions, the soft lateral membranes evidently vary, some having the outermost 

 refractive layer thrown up into papilla, others into irregular (?) longitudinal foldings. 



Set(B and Spines. — The Galeoclidse are remarkable for their rich covering of seta?, 

 i^pines, &c. These attain their greatest develoi^raent, as a rule, on the limbs. Com- 

 mencing with the short stunted spine standing up from the hollow of a ring of thick red- 

 brown chitin and itself bright red-brown (PI. XXX. fig. 8), we have short stiff setEe with 

 blunt, slightly forked ends *, and thin flexible setse tapering finely to a point, and often 

 attaining an extraordinary length (PI. XXIX. fig. 3), club-shaped setse, &c. Most of the 

 seta3 show a disposition to form regular rings which, when further developed, might lead 

 to the feathering which cliaracterizes certain setiB on the chelicerje and beak. The 

 setae, as such, require a careful study, in order to ascertain their special physiological 

 significance. 



The attachment of the seta? to the cuticle is apparently uniform ; I could find no difference 

 between the method in which the spines and the finer seta? were fixed in the cuticle. Ail 

 alike are suspended by the outermost hard or glassy layer, which runs over tliem as an 

 outer covering. The figures (PL XXX. figs. 4-8) will explain what I mean by " suspended." 

 The setse rise from the bases of hard cbitinous craters, there being no break in the continuity 

 of the outer refractive layer t- On the other hand, the inner softer cbitinous layers are 

 not continuous -^vith the inner lining of the setfe, but the two are connected by numberless 

 fine radiating fibres (;/.) which, like all flexible chitin, take stain, while the layers which 

 they connect often I'emain unstained. These radiating fibres either bring about by their 

 active contraction, or else restrain by their elasticity, the play of the seta. Radiating from 

 the extreme butt-end of the seta to the walls of the chamber, they completely divide it into 

 an upper and lower portion. In the long sensory setae on the limbs the upper chamber 

 communicates with the cavity of the body by a separate channel {cf. c on PI. XXX, 

 fig. 7«; PI. XXXII. figs. 13, 11). 



In order to make room for the play of the butt-end of the seta, the channel throuo-li 

 the cuticle is enlarged in various ways. Where the cuticle is thick, the setal pore widens 

 out suddenly, the staining fibres radiating from the shelf thus formed, the widened area 

 being lined by a layer of hard refractive chitin (PI. XXX. fig. 1). When the cuticle 

 is thin, the hard refractive chitin forms a sort of globular chamber into which the base of 

 the seta is suspended in the usual way, the chamber being often much deeper than the 

 surrounding cuticle (fig. 5). The strong chambers prevent the sera from being foi'ced 

 back into the tissues of the animal. There is a further precaution against the same 

 danger in the case of the sjnnes, inasmuch as they widen out, spear-head-shaped, above 

 the ramparts surrounding their bases (fig. 8). 



The setae at the tip of the labrum are specially modified. They are joined by short 

 trabeculse so as to form a stiff' rectangular lattice-work (PL XXVIII. fig. 6). They form 

 tw'o series arranged on each side of the mouth and running dorso-ventrally. As the tijis of 

 tlie setae are feathered and the barbs interlace, the arrangement forms a sieve to prevent 



* In ' Nature ' (vol. xlvi. p. 223, 1892) I compared these to buttoned rapiers. 



t Wagner's account of the connection between the setas and the cuticle in Spiders (74) differs from this. 



