366 Prof. E. Ray Lankester on the 



tostraca and Limulus ; 2, Aerobranchia, including the Scor- 

 ])ions and Spiders ; and 3, Lipobranchia, including the 

 Pseudoscorpiones, Galeodes, the Opiliones, and Acarina. 



II. Prof. Clans says, " the class Arachnoidea, the starting- 

 point of which must probably be sought in the great Palajo- 

 zoic Gigantostraca with their resemblance to the Scorpions, 

 hitherto regarded as Crustacea upon insufficient grounds." 



It would be more correct to say, " hitherto regarded by 

 Professor Clans as Crustacea upon insufficient grounds," since 

 the close affinity oi Limulus and the Gigantostraca to the Scor- 

 pions was demonstrated inmy memoir "Limulus an Arachnid," 

 published as long ago as 1881. The whole purpose of that 

 memoir was to establish this close affinity. That purpose 

 was effected by a detailed comparison of segment with seg- 

 ment and organ with organ in the two series of Arthropods 

 compared. I showed not only that the segments agreed with 

 one another in Limulus and the Scorpion, but that the position 

 and modification of such important parts as the genital oper- 

 eula is actually coincident, and that the chilaria (metastoma) 

 of Limulus and the Gigantostraca (often erroneously reckoned 

 as modified limbs) are identical with the metasternum of 

 Scorpio. I was able to show that the gill-books of Limulus 

 agree in structure and position with the pectines and the 

 lung-books of Scorpio. I have since, in other memoirs, de- 

 monstrated the exact equivalence in minute structure and 

 general relations of (1) the internal cartilaginoid sternum 

 or entochondrite of Limulus, Scorjno, and Mygale (Quart. 

 Journ. Micr. Science, January 1884); (2) of the lateral and 

 central eyes of Limulus and Scorpio (Quart. Journ. Micr. Sci. 

 January 1883) ; and (3) of the coxal glands of Limulus with 

 the similar glands discovered by me in Scorpio and Mi/gale 

 (Quart. Journ. Micr. Sci. 1884, and Proceed. Roy. Soc. 

 1882). Other points of agreement I have also insisted upon 

 in the above memoirs, and in one just published by the Zoo- 

 logical Society of London (Trans. Zool. Soc. vol. xi. 1885), 

 which I will not here further enumerate. 



It seems to me an extraordinary thing that Prof. Claus 

 should omit all reference to these published researches and 

 the conclusions formulated by me, and should declare that 

 " hitherto" (that is to say until the publication of his Note 

 in the 'Anzeiger ' of the Imperial Academj^) the Palseozoic 

 Gigantostraca have been regarded as Crustacea. 



III. Professor Claus proceeds further to say: — "Hitherto, 

 evidently, far too much stress has been laid upon this last 

 agreement [viz. branchial respiration] in the division of the 

 Arthropoda into Branchiata and Tracheata, without taking 



