COMPAEATIVE MOEPHOLOGT OF THE GALEODID.E. 355 



These last-described organs, which ajipear to be the commonest forms, were not found 

 on the first leg of the small llhax above referred to (PI. XXXII. fig. 10). 



Lyriform Organs. — I have been able to confirm Hansen's description (33) of the 

 group of slit-like markings at the ventral edges of the chelicerse. These were the only 

 organs of the kind Hansen succeeded in finding in the Galeodida?. I have also 

 accidentally found an isolated lyriform organ among the hairs on the ventral side of 

 the first leg of a Galeudes. I have made no special search for them. What these 

 organs are, morphologically and physiologically, is at present imknown. I would 

 suggest their probable derivation from setal pores. 



As evidence iu favour of this explanation of tlie lyriform organs, the following points deserve 

 attention : — 



1. These lyriform organs, when simple, not only agree in size with the setal pores, but also show the 

 same variations in this respect as do the setal pores. 



2. They occur singly or iu scattei'ed groups, the individual members of which either vary or agree in 

 size, or, lastly, in closely-arranged groups. 



3. They occur in jjlaces where hairs generally occur or might be expected to occur, and often among 

 the hairs. In the latter case their size agrees well with that of the adjacent setal pores. 



4. They sometimes appear to run iu rows parallel with rows of hairs, and where they occur it looks 

 as if a row of hairs was wanting. 



Iu addition to these arguments, I would point to the pores which appear to open at and round the 

 tips of the mandibles of Gal codes. These seem to be open, owing, perhaps, to the wearing away of the 

 hard outer layer of the cuticle ; and if so they may account for the poisonous character attributed by 

 many persons to their bite. These pores are certainly setal. 



There is no inherent difficulty iu this suggestion ; as a seta aborts, the pore with the nerve which 

 once ran to the seta might jjersist and be adapted for other purposes. 



On the other hand, however, I have found " lyriform organs ■" which have not so arisen. On 

 the coxa of the last leg of a small Tliehjphonus , zigzag cracks occur iu the thick chitin, many in 

 the shape of an open W. Setfe often occurred near them. Close examination showed that iu the 

 angles of the zigzag came the corners of the polygonal cells of the tesselated hypodermis. These organs, 

 then, were merely slits iu the chitin between the seereting-cells. I could see the nerve-fibres running 

 among the hypodermis cells, but the chitin of these slits was so dense and refractive that it was 

 impossible to see whether a nerve came to the surface between them or not. I think it is almost 

 certain that they are sensory organs of some, perhaps very simple, kind. 



These organs, which certainly do not rise from setal pores, do not alter my view that the ordinary 

 lyriform organ with a cylindrical channel through the chitinous cuticle, as occurring on the underside 

 of the chelieer?e of Galeodes, did arise in the way above suggested. 



VIII. The Alimentary Canal. 



The Mouth and Q^sojjhagus. — The mouth, as has already been described, is situated at 

 the end of a beak, and is guarded by an elaborate sieve-like arrangement of bristles 

 (PI. XXVII. fig. 11, PI. XXVIII. figs. 5, 6). It opens into a long oesophagus, which 

 runs through the beak and passes through the ganglionic mass to enter the mid-gut. 

 Within the beak the oesophagus, which in transverse section is triangular with the apex 

 pointed downwards (PI. XXVIII. fig. 3), can be alternately expanded and contracted, by 

 means of a system of radiating and circular muscles, making thereby a sucking-apparatus 



47* 



