154 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Comparative Anatomy of the Arachnida," read to the Academy of Sciences June 1, 1829, but never, I believe, pub. 

 lished. M. Strans Durckheim communicated its contents to MM. Reister and Sanson. From this note I submit a few 

 extracts. The authors commence : 



"La classe des Araehuides, dans laqnelle M. Straus comprend le genre Limule, formant a, lui-seul un ordre design^ 

 sons le nom de Gnathopodes et dont il isole les Pycnogonides qu'il renvoie aux (Jruatac^es, oifre dans la disposition de 

 son squelette et des muscles qui en meurent les diverges pifeces. des particularit^s tellement trauch6es qu'onne pent, 

 y m^connaltre uu type different. C'e.st de ce squelette que sout tir^s les traits principaux propres ^ caracteriser la 

 classe des Arachnides en g6u6ral, et qui consiste dans la disposUion des pattes raijotinunt siir un steniiim cominnn,dans la 

 presence d'liii sfeniiim carlUafilneur intdrieur, dans Vahsence d'antennes." 



The Arachnida are then divided into three orders, "les pulmonaires, le^branuhifiires, et les trach^ens," but it is 

 not explained whether the term "gnathopodes" Is to be regarded as simjjly a synonym of the order " branchif feres." 



With regard to the internal sternum, the citation of the views of M. Straus runs as follows: 



"Dans I'int^rienr du thorax de tons les Arachnides, h I'exceptiou peut-etre des Acarides dont la plupart des espfeoes 

 sont trop petites pour qu'on puisse les dissequer et connaltre leur organisation, on trouve une pifece cartilaginense 

 diversemeut configur(5e suivaut les families, et plac^e dans le thorax on dessus du sternum, cette pifece, a. laquelle con- 

 vient le nom de sternum iut^rieur, est maintenue librement par le moyen de plusiers muscles qui ce conduit de diff^- 

 rents points de sa surface sur le bouclier, on sur le sternum ext^rieur auquel ils se fixent. Elle sert en outre de point 

 d'insertion ^ un certain uombre de mu.scles des pattes." 



In Cuvier's Efegue Animal, uouv. 6dit., 1829 (torn, iv), tbe group named by Latreille, Poeeilopoda, 

 i s characterized and described a.s the second order of Entomostraca. The order consists of two fami- 

 lies: Xiphosura (genus Limulus) and Siphonostoma (Caligus, Argulus, etc.). As the group Poeeilo- 

 poda, by its founder, includes the parasitic Copepoda besides Limulus, it seems advisable to drop 

 it, retaining the term Xiphosura, which has never been applied to any other animal than Limulus 

 and its allies. On p. 46 he remarks: "De cet ordre de crustaces on arrive a la classe des Arach- 

 nides, dont I'organisation, en g^n^ral, approche beaucoup de celle des Limulus." 



In 1830 Milne-Edwards (Ann. des Sc. Nat., xx. mars 1830) adopted the order Xiphosura, 

 placing it below the Siphonostomata. 



In 1834: Milne-Edwards (Hist. Nat. des Crustaces) retained the order Xiphosura. 



StrausDiirckbeim's views were more explicit than supposed by Professor Lankester, as in 

 Straus's work, published in 1842, entitled " Traite pratique et th^oretique d'Anatomie compara- 

 tive," etc., vol. 2, 169, we find the following statement : 



J'ai form6 I'ordre des Gnathopodes avec le seul genre LiniiiUis. Cus siuguliers animaux out 6t6 rangfc parmi les 

 Crustaces par tons les naturalistes ([ui, ue connaissant pas lear organisation, les plafaient dans cette classe par cela 

 seul qu'ils out des branchies, tandis (lu'ils s'en distinguent essentiellemeut par le reste de leur organisation, en offrant 

 les plus graudes analogies avec les Ara.hnides S et ('existence des. branchies ue saurait a elle seule constituer un 

 caractfere snffisant pour les Eloigner de oes derniers, vu que dans cette classe les organes de la respiration u'ont plus 

 cette grande preponderance sur les autres appareils du corps, pour les tenir sous leur d(5pendance, comme cela a lieu 

 chezles vertebras; ce qui est prouv^ par I'analogie qui existe eutre les Arachnides pulmonaires et les trach^ens, qu'on 

 ne saurait s^parer. 



Dana (1852) in his Crustacea of the U. S. Exploring Expedition, proposed the order Merosto- 

 mata for Limulus exclusively, which he places in the tribe Limuloidea. He makes no mention of 

 the Eurypteridie. The Fcecilopoda in Dana's system forms the first suborder of Gormostomata, and 

 fnclude the Ergasiloidea, Caligoidea, and Leruisoidea. 



In 1866 Hi^ckel (Generelle Morphologic der Organismen, ii, Ixxxix) regarded the Trilobita as 

 forming the third legion of Branchiopoda. They are in his system succeeded by the sixth subclass 

 of Crustacea, the Poeeilopoda, which embraces the two legions of Xiphosura and Gigantosiraca. The 

 latter name is proposed for the Pteri/gotidw and Euryptcridw alone. As Hfeckel's Gigantostraca 

 appears to be exactly synonymous with Dana's Merostomata as amended by Woodward, tbe awk- 

 ward, meaningless term, which has never been defined, should be discarded. It has, however, 

 been adopted by Dohrn in 1871 (Zur Embryologie uud Morphologic des Limulus Polyphemus, 

 Jena. Zeits, vi, 1871), and by Chins, though in a greatly extended, and it seems to us an unwar- 

 rantable, sense. Dohrn remarks: 



Limulus is nearest related to the Gigantostraca. Both appear to be "related to the Trilobites, though this rela- 

 tionship cannot be established in all the details. The morphological ami genealogical relations of these three fami- 

 lies to the Crustacea are not such as to be surely determined ; perhaps they will remain always doubtful. That they 

 are related to the Arachnida we are not, as the matter now stands, in a position to allow. So it only remains for us 

 to put these three groups under a common name, for which I might adopt Haeckel's expression "Gigantostraca," and 

 let.them take their place in the system with {nehen) the Crustacea. 



