IV. 



Further Notes upon the Organs of Arachnids. 



IN an article contributed to Natural Science (vol. iii., p. 441) at 

 the end of last year, and in some previous reviews therein 

 mentioned, I endeavoured to trace the Hght thrown by recent 

 researches upon the structure and relationships of the spiders and 

 their allies. Several fresh memoirs upon the subject have appeared 

 during the year now passing away, and some account of these also 

 may prove of interest. 



A question discussed in several of my previous reviews was 

 whether lung-books or tracheal tubes are to be regarded as the older 

 form of breathing organ among the arachnids. The majority of 

 modern naturalists, following Professor Ray Lankester in considering 

 Limuhis a marine arachnid of ancient type, believe the lung-books of 

 scorpions and spiders to have been formed by the inpushing or 

 sinking of the gill-bearing limbs of a water-breathing ancestor, and 

 the tracheal tubes found in the higher spiders and other arachnids to 

 have been derived by the simplification of such lung-books. The 

 opposite view is maintained by Mr. H. M. Bernard, who, considering 

 Limulus a " specialised crustacean," sees in the tracheae of arachnids 

 the representatives of the original series of ventral setiparous glands 

 in a hypothetical worm-like ancestor, and believes that lung-books 

 are a new development from the tracheae. In support of this idea 

 Mr. Bernard has in several recent communications (i, 2,3) announced 

 the discovery in the Chernetida (false-scorpions) of a series of paired 

 vestigial stigmata on all the abdominal segments behind the fourth 

 (the functional stigmata leading to the tracheal tubes being found on 

 the third and fourth abdominal segments). Unfortunately, however, 

 this observation has been severely called in question by Dr. H. J. 

 Hansen, who, in a discursive paper of considerable interest (4), 

 dismisses the "vestigial stigmata" as nothing but lyriform organs 

 {see Nat. Sci., vol. i., p. 525), of which he finds not a pair only, but two 

 pairs on each abdominal segment. Mr. Bernard, in his latest paper 

 on the subject (5), returns undaunted to the charge, and expresses his 

 conviction that the objects under discussion are not lyriform organs. 

 He admits, however, that there are two pairs of them on some 

 segments, and suggests that if one series represent vanished stigmata, 

 the other may be the vestiges of former spinning or cement glands. 



