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.
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