342 Proceedi.iKjsi of the Royal Triah Academy. 



('91) seems likely, altKough the fact that they sink into pits and. 

 occupy the position of the cheliceral ganglia, makes his intei'pretation 

 uncertain. The pre-antennal segments that he described later ('92) 

 do not seem to rest on very clear evidence ; vhile the two pairs of 

 vestigial appendages lately described and figured by Pokrp-^sky ('99), 

 in the embryo of Pholcus, are not convincing. But the presence of a 

 pre-cheliceral segment is clearly indicated by the segmentation of the 

 Scorpion's brain as interpreted by Brauer ('95). Anterior appendages 

 are perhaps to be found in the paired rudiments of the rostrum, as 

 suggested by Croneberg ('80). These are conspicuous in the embryo of 

 Trochosa rwricola (fig. 5), Tvhich I have examined in the vain hope 

 of seeing Jaworowski's antennse. They are also clearly shown in 

 Brauer's figures of the embryo Scorpion, ultimately becoming fused 



Fig. 5. Front portion of germ-band of Trochosa ruricola ; ro., ch., pip., 1., rudi- 

 ments of rostrum, chelicerae, pedipalps, and first pair of legs; ch.. g., 

 cheKceral ganglion: I.e., lateral eyes, x 28. 



togethei. Lendl {fide Korschelt ('99)) has described vestigial appen- 

 dages between the chelicerae and the pedipalps of Spiders. The 

 former existence of a limb-bearing segment there is indicated by the 

 structiu-e of the Pycnogonida, which seem to be an aberrant order 

 of Arachnida. ISot only do the embryologieal history, as described 

 by ITorgan ('91), the possession of chelicerae as the foremost pair of 

 limbs, and the four pairs of walking-legs suggest Arachnid affinities, 

 but also the fact that the segments bearing the three hinder pairs of 

 legs are, in the generalized families of Pycnogonida, as in the 

 Solifugida, not fused with the cephalic segment on which the four 

 front pairs of limbs are borne. This indicates that the pycnogonid 

 appendages, not present in Arachnida generally, are the palps. 

 Therefore, it is safe to conclude that the Arachnidan head with three 



