422 COMPARATIVE ANATOMY CHAP. 



J. Barrande. Systeme silurien du centre de la Boheme. Vol. I. Prague, 1852. 



Supplement. 1874. 

 J. W. Salter and H. Woodward. A Monograph of British Trilobites. Palcconto- 



grapliical Society, 1867-1884. 

 Fr. Schmidt. Revision der ostbaltischen silurischen Trilobiten. 1. Him. de I'Acad. 



imp. de St. Petersburg. Ser. VII, tome 30. 1881. 

 C. D. Walcott. The Trilobitce. New and old evidence relating to its organisation. 



Bull. Mus. Comp. Zoology, Cambridge, Mass. Vol. VIII. 1881. 



Gigantostraca and Hemiaspidse. 



J. Nieszkowski. Der Eurypicrus remipes aus den obersilurischen Schichten der 

 Insel Oesel, in Archiv f. Naturgeschichte Liv-, Est-, und Kurlands. 1. Ser. 

 2. Band. 1859. 



H. Woodward. A Monograph of British fossil Crustacea belonging to the order 

 Mesostomata. Palwoniographical Society. Parts I-V. 1866-1878. 



Works of Huxley, Salter, Woodward, Baily, Schmidt, etc. 



Xiphosura. 



Alph. Milne-Edwards. Eecherches sur I' Anatomic des Limules, in Ann. Sciences 



naturelles, 5 serie, t. XVII. Paris, 1873. 

 A. J. Packard. The Anatomy, Histology, and Embryology of Limulus polyphcmus, 



in Mem. Boston Society Natural History. Boston, 1880. 

 E. Ray Lankester. Limulus an Arachnid, in Quart. Journ. Micr. Science, vol. 



21. London, 1881. 

 J. S. Kingsley. Notes on the Embryology of Limulus, in Quart. Journ. Micr. 



Science, vol. 25. London, 1885. 

 Treatises of J. van der Hceven, Gegenbaur, Packard, Dohrn, R. Owen, Gulland, 



etc. 



Second Appendage to the Class of the Crustacea 

 The Pantopoda (Pyenogonidse). 



The body, in comparison with the long and slender limbs, is 

 extremely reduced, and falls into three divisions proboscis or beak, 

 trunk, and hind -body. The proboscis articulates with the most 

 anterior trunk segment. At its point lies the mouth surrounded by 

 three lips, and it contains internally the greater part of the fore-gut 

 (" fish trap " apparatus). It consists of three pieces lying side by side 

 longitudinally, an upper median piece and two lower lateral pieces. 

 The trunk consists of 6 segments, the three anterior of which are 

 always fused together ; it has lateral outgrowths on to the ends of 

 which the limbs are hinged. The hind-body is unsegmented, short, 

 truncated, and devoid of limbs. 



Extremities. 7 pairs of extremities occur typically. The first 

 extremities (1), the chelicerse, are innervated from the brain, and in 

 the young animal end in pincers ; in the adult they are often reduced 

 or altogether wanting. The following extremities (2-7) are inner- 

 vated from the ganglia of the ventral chord, 2 and 3 from the most 

 anterior ganglion, which consists in the larva of two separate ganglia. 



