4 A. S. PACIvARD, JR., ON THE ANATOMY 



Straus-Dlirckheim was the first author to remove the genus Limulus from the 

 Crustacea, and to regard it as the type of a distinct order of Arachnida, which he called 

 Gnathopodes. In his memoir, published in 1829, according to Van der Hoeven's statement, 

 Straus characterized the Arachnida by the disposition of the feet arranged in a circle 

 around an interior cartilaginous sternum, and by the absence of antennae. Van der 

 Hoeven, in 1838, remarks that the branchiae are the principal characters of Crustacea, 

 as insisted upon by Latreille and Milne-Edwards, who placed Limulus in this class ; 

 therefore Limulus should belong with these animals, and he shows that there are other 

 characters which separate Limulus from the Arachnida, and which ally them with 

 the Crustacea. These are the compound eyes, the position of the stomach in the 

 front of the cephalothorax, " while it is contained in the abdomen of Arachnida." He 

 then says : " But whether we place the Limuli among the Crustacea, or with the 

 Arachnida, they should always form a distinct order for themselves alone, which, in 

 the actual state of our knowledge, is far from all the other orders of these two classes." 

 Afterwards, in 1846, in his Handbook of Zoology, and again in the second, English 

 edition of 1856, he placed the Poecilopoda as the first order of Crustacea, referring, 

 however, to their resemblance to Arachnida. 



In 1871, Dr. A. Dohrn, in his Untersuchungen liber den Bau und Entwicklung der 

 Arthropoden, concluded that Limulus, Eurypterida and Trilobita should be united un- 

 der a common name, Gigantostraka, as originally proposed by Haeckel, in his Mor- 

 phologic, for the Eurypterida alone ; and that they should be placed near the Crus- 

 tacea. 



Most if not all the other leading zoologists, while recognizing the aberrant characters 

 of the Limuli, have left them among the Crustacea, though in 1834 H. Milne-Edwards 

 established a subclass (Xiphosura) for the group ; this group being equivalent to 

 any one of several other subclasses of Crustacea which he envimerates. For the views we 

 held previous to the publication of H. Milne-Edwards' memoir, we would refer the 

 reader to our Memoir on the development of Limulus, published in March, 1872. 



In October, 1871, the following views of M. Edouard Van Beneden^ were published : 

 " L' etude du developpement embryonnaire de ces animavix et de leurs caracteres 

 anatomiques m'a conduit aux conclusions suivantes que je puis formuler des a present : 



I. Les Limules ne sont pas des Crustaces ; ils n'ont rien de commun avec les 

 Phyllopodes, et leur developpement embryonnaire presente les plus grandes analogies 

 avec celui des Scorpions et des autres Arachnides, dont on ne pent les separer. Dans 

 le cours de leur developpement embryonnaire, on ne distingue aucune des phases 

 caracteristiques du developpement des Crustaces, et il ne peut etre question de distinguer 

 dans le cours de ce developpement embryonnaire, ni phase nauplienne, ni phase 

 cyclopeenne. 



II. L'analogie entre les Lirhules et les Trilobites, et I'affinite qui relie entre eux 

 ces deux groupes, ne peut etre un instant douteuse pour celui qui a etudie le 

 developpement embryonnaire de ces animaux. Les lois de developpement sont les 

 memes chez les Trilobites et les Xiphosures, et l'analogie entre les jeunes Trilobites et 



1 Journal de Zoologie. Par Paul Gervais. Tom. I, p. 42, 1872. Paris. 



