1881.] 



On Stigmata in the King Crab. 



391 



X. " Note on the Existence in the King Crab (Limulus poly- 

 phemus) of Stigmata corresponding to the Respiratory 

 Stigmata of the Pnlmonate Arachnida, and on the Morpho- 

 logical Agreements between Limuhis and Scorpio." By E. 

 Ray Lankester, M.A., F.R.S., Jodrell Professor of Zoology 

 in University College, London. Received May 26, 1881. 



I. — The Agreements between Limulus and Scorpio. 



The conclusion arrived at by Straus Durckheim (1828) to the effect 

 that Limulus is an Arachnid, and as such to be placed in a distinct order 

 of the class Arachnida, has not as yet been generally accepted by zoolo- 

 gists. It is, however, to be noted that whilst the zoologists of the first 

 half of this century had no hesitation in placing Limulus among the 

 Crustacea, and even in associating it in one order with such Crusta- 

 ceans as the Phyllopoda, yet there has been an increasing tendency 

 within the last five-and-twenty years to recognise very distinctly 

 something like affinity between Limulus and the Arachnida. This 

 tendency has shown itself in the proposal made by some eminent 

 authorities of late (Haeckel, Dohrn, Claus, Gegenbaur) to place 

 Limulus in a distinct group by itself ( Gigantostraca or Pcecilopoda), 

 neither Crustacean nor Arachnidan, but nearly equally removed from 

 and equally related by supposed genetic connexions to both the 

 Crustacea and the Arachnida. Professor Edouard Van Beneden, ot 

 Liege, alone, professedly basing his conclusion upon an examination of 

 the embryological history of Limulus, has categorically declared that 

 " the Limuli are not Crustacea ; they have nothing in common with 

 the Phyllopoda, and their embryonic development presents the greatest 

 analogies with that of the Scorpions and of the other Arachnida, from 

 which it is not possible to separate them." 



I have elsewhere* stated my full concurrence with Professor Van 

 Beneden's conclusion on this subject, and proposed accordingly to 

 divide the Arachnida into the Branchiopulmonata and Tracheopul- 

 monata, but I have not hitherto taken an opportunity of setting forth 

 the grounds upon which I am led to hold that the Limuli are Arach- 

 nida and not Crustacea. These grounds are entirely independent of 

 those advanced by Professor Van Beneden, which were derived from 

 the phenomena of embryonic development. The grounds upon which 

 I base my conclusions are, on the contrary, found in the facts of the 

 adult structure of Limulus on the one hand and of the pulmonate 

 Arachnida on the other, more especially of Scorpio. 



I have recently become acquainted with some undescribed struc- 



* "Notes on Embryology and Classification." " Quart. Journ. Micr. Science," 

 October, 1877. 



