Mr. A. S. Packard, Jim , on Limulus. 369 



XXXVII. — Is Limulus an Arachnid? 

 By A. S. Packard, Jun.* 



In an article by Professor E, R. Laukester in the ' Quarterly 

 Journal of Microscopical Science ' for July and October 1881, 

 entitled '^Limidus an Arachnid," the author, distinguished 

 for his histological and embryological papers especially re- 

 lating to Mollusks and Coelenterates, takes the ground that 

 LimuluSj or the horseshoe or king crab, " is best understood 

 as an aquatic scorpion, and the scorpion and its allies as ter- 

 restrial modifications of the king crab;" and on p. 507 he 

 makes the following startling announcement : — " That the 

 king crab is as closely related to the scorpion as is the spider, 

 has for years been an open secret which has escaped notice 

 by sometliing like fatality." While appreciating the thorough 

 and critical nature of tlie learned author's work, especially 

 observable in his excellent paper on the structure of Apus, 

 we venture to assert that in regard to the systematic position 

 of Limiiljis Professor Lankester has mistaken interesting 

 analogies for atlinities, and has on quite insufficient and at 

 times wholly hypothetical grounds rashly overlooked the 

 most solid facts and safe inductions from such facts, and 

 arrived at very forced and, it seems to us, strange and quite 

 untenable conclusions. 



At the outset it will be remembered that Limulus differs 

 from the Tracheates, including the Arachnids, in having no 

 tracheae, no s])iracles, and no Malpigliian tubes. It differs 

 from Arachnids in these characters, also in having compound 

 eyes, no functional mandibles or maxillae, the legs not termi- 

 nating, as is generally the case in Tracheates, in a pair of 

 minute claws ; while its brain does not, as in Arachnida, 

 supply both eyes and first cephalic appendages. On the 

 other hand, Limulus agrees with Crustacea in being aquatic 

 and breathing by external gills attached to several pairs of 

 biramous feet ; in having a simple brain, which, as in some 

 groups of typical Crustacea (Branchiopoda, &c.), does not 

 supply any of the appendages, while the structure of the cir- 

 culatory, digestive, and reproductive organs agrees with that 

 of the Crustacea; and, as we have shown in our "Embryo- 

 logy of Limulus^^ ('American Naturalist' for 1870), the 

 development of Limulus is like that of certain other Crus- 

 tacea with a condensed metamorphosis, the possession of an 

 amnion being paralleled by that of Apus. In all essential 

 points Limulus is a Crustacean, witli some fundamental fea- 



* From the ' American Naturalist,' April 1882. Coinmunicated by the 

 Author. 



