322 MBMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 



me that the book-leaves of Arachuida are really the homologiies of the thin gill-sacs of Limulus, aud 

 that the two classes have probably originated, if not from a common ancestor, yet from those stand- 

 ing very near each other. 



In closing, we would make a suggestion in the way of an explanation of the points of resem- 

 blance of the Podostomata (Merostomata and Trilobites) to the Phyllopod Crustacea, especially 

 Apus. Even so strong an opponent of the idea that there is any close affinity between Apus and 

 Limulns as Lankester, allows that there are some points of resemblance between Apus and Limu- 

 lus, " the most important being the jaw-processes at the base of all the ambulatory limbs, and the 

 presence of a- pUre archicerebrum in both genera." 



We have shown that the brain of Limulus, though roughly speaking an archicerebrum, is 

 veiy different from that of any Phyllopod. StiU the points of resemblance between these 

 primitive Phylloi^ods and the Merostomata are due, perhaps, to the fact that the ancestors of both 

 Crustacea and Podostomata were probably derived from somewhat similar Annelid-like ancestors, 

 though by quite independent lines of descent. We would therefore agree with Lankester's con- 

 clusion in his essay on Apus, that the points in which Apus and Limulus agree " are probably 

 points in which they both approach the common ancestor of the Arachnida and Crustacea." 



But we differ from this able author in supposing that the Merostomata and Trilobites, or at 

 all events the Merostomata, should be merged with the Arachnida, as they have characters,' both 

 external and internal, which forbid their being regarded as Arachnids. 



We believe, with A. Milne Edwards, that they should form a separate class. There were, then, 

 four lines of development in the Arthropoda (throwing out for the present the Liiiguatulina and 

 Tardigrada), viz: The Podostomatous line, the first to be struck off from the Annelidan stock (the 

 trilobiti's being the first forms to appear), second the Ai-achnidan line; tliird, the Crustacean line, 

 nearly coeval with the first or Podostomatous; and the fourth, the line culminating in Myriopods, 

 Scolopendrella, and insects; and it is safe to suppose that the terrestrial tracheate groups of Arach- 

 nida, Myriopoda, and insects were later products than the marine, aquatic branchiate classes, 

 i. e., the Podostomata and the Crustacea. 



LITEKATURE BEARING ON THE SUPPOSED HOMOLOGY OF THE UUANCllIAL APPENDAGES OF LIMUH'S AND THE B1!UK- 

 LUNGS OP ARACHNIDA. 



Bali'Ouk, F. M. Notes on the development of the Araneina. Cjuart. Jour. Micr. Science, xx, 1880. 



Meknard, }I. M. An entleavor to show that the trachete of the Arthropoda arose from setiparous .sacs. Spen- 

 gcl's Zodl. Jahrbuch, pp. 511-524, 1892. 



Bertkau, Ph. Ueber die Respirationsorgane dor Aranoen. Arch, fiir Natui'geschichte, 38. Bd., 1872. 



KiNGSLEY, J. S. Notes on the embryology of Limulus. Quart. Journ. Micr. Science, xxv, 1885. 



KisHinouye, K. On the development of Araneina. .Jour. College of Science Imp. University, Japan, iv, 1890. 



. On the development of Limulus longispina. Ibid. v. 1891. 



Lankester, E. R. Limulus au Arachnid. Quart. Jour. Micr. Science xxi, 1881. 



. New hypothesis as to the relationship of the lung-book of Scorpio to the gill-book of Limulus. Quart. 



Jour. Micr. Science, xxv. p. 339-342, 1888. 



Laurie, M. On the development of the lung-books in Scorpio fulvipes. Zool. Anzeiger, xv. Jahrg., No. 386, 14 

 Miirz, 1892. 



LoCY, W. A. Observations on the development of Agelene najvia. Bull. Mus. Comp. Zool. xil, 1886. 



MacLEOD, J. Recherches sur la structure et la signification de I'appareil respiratoire des Arachnides. Archives 

 de Biologie, Gand, Tome v, 1884. 



Milnk-Edwards, a. Recherches sur I'anatomie des Limulus. Anuales des Sciences Naturelles, aine Scr. Zoulo- 

 gie, xVii, 1873, Paris. 



Metschnikoff, E. Embryologie des Scorpions. Zeit. fur Wissensch. Zoologie xx, 1870. 



Patten, W. On the origin of Vertebrates from Arachnids. Quart. Journ. Micr. Science xxxi. New Ser. 1890. 



Salensky, W, Embryology of the Araneidic. Mem. (Sapisky) Kieff Soc. of Naturalists, li, Pt. 1, pp. 1-72, PI. 

 i-iii. 1871, Kieff, 1871. (Russian). Abstract in Jahresb. iiber Auat. u. Physiol. (Hoffmann u. Schwalbe), Bd. ii, 1873, 

 pp. 323-325, 1875. 



Schimkewitsch, W. Etude sur le d^veloppement des Araign^es. Archives de Biologie, vii, 1885. Brnxelles. 



Van Beneden, E. De la place que les Limules doivent occuper dans la classification des Arthropodes. C. R. 

 Soc. Ent. de Belgique. Oct., 1871. (Ann. aud Mag. Nat. Hist. 1872.) 



. Sur la structure et la signification de I'appareil respiratoire des Araclmides. Bull. Scient. Di:'part. 



du Nord, 5 'ann., pp. 299-301, 1882. 



Walcott, C. D. The TrUobite : New and old evidence relating to its organization. Bull. Mus. Comp. Zool. viii, 

 1881. (See also Waloott's article issued in advance of the 28th Report of New York State Museum of Nat. Hist 1876, 

 also the 3l8t Report of the same museum.) 



