PROFESSOR OWEN ON LIMULUS POLYPHEMUS. 195 



closing posteriorly the circumoral armature. The serial homology of the chilarian with 

 the palpal nervules lends some countenance to that of the appendage, so supplied, being 

 a detached spinigerous process or ' palpus ' of vn." 



[Referring elsewhere (at p. 464) to this pair of compressed spinigerous oblong plates, 

 situated immediately behind the sixth pair of circumoral apppendages, and closing as it 

 were the buccal orifice behind, Professor Owen observes " they recall to mind the 

 pectinate appendages of the thoracetron in Scorpio. In Limulus they close or complete 

 the oral armature posteriorly, forming the ' levre inforieure ' of Cuvier, and a correspond- 

 ing member of the ' trophi,' according to Savigny ; but Latreille preferred to regard them 

 as the haunches or jaw-lobes of the sixth pair of limbs detached. The haunch-joints, 

 however, are present, though less dentated in the sixth pair of appendages (PI. XXXIV, 

 fig. 4, lp). The appendages in question have their own distinct pair of nerves 

 (Pis. XXXIV and XXXV, fig. 1 n*) arising between the origins of the main nerve of the 

 limb (vn) and that of the ganglionic chord, suggestive of a serial homology with the 

 palpal nervules. I am not," he adds, "however, satisfied with this as a ground for 

 regarding the parts in question as detached limb-palps ; and I therefore propose to call 

 them ' chilaria ' " (from ytikapiov, a small lip). 



Vander Hoeven refers to them as " the two pieces placed behind the sixth pair of 

 feet, and which some authors consider as forming the lower lip." 1 



Huxley considers it " the rudimentary metastome," and, referring to the variation which 

 the plate undergoes, mentions that " in Calanus it is excavated anteriorly by so deep and 

 wide an emargination, that it almost appears to consist of two distinct lobes. In 

 Po?itella, on the contrary, the metastoma is a large flattened plate, whose terminal 

 emargination, though wide, is not deep. 3 



I have invariably adhered to this view of the ' chilaria ' in Limulus. Indeed, there 

 seeing no reason to doubt that this pair of oval oblong plates, the bases of which are 

 united on the median line of the body, represents the inferior lip, and is homologous 

 with the great conjoined but bilobed metastomatal plate placed precisely in the same 

 position behind the mouth in Eurypterm and Pterygotus, 5 and I find that the researches 

 of my distinguished friends, Dr. Anton Dohrn* and Dr. A. S. Packard, jun., 5 into the 



1 J. vander Hoeven, ' Recherches sur l'Histoire Naturelle et l'Anatomie des Limules,' Leyien, 4to, 

 1838, p. 48, 7 plates. 



3 'Medical Times and Gazette,' 1857, vol. xv, p. 188; 'Mem. Geol. Surv.,' Mon. I, 1859, "On the 

 Anatomy and Affinities of the Genus Pterygotus" pp. 33 and 34. 



3 See 'British Assoc. Reports' for August, 1871, on "The Structure of Fossil Crustacea;" also 

 'Geol. Mag.,' 1871, vol. viii, p. 524. See also Parts I — IV of this Monograph. 



4 " Zur Embryologie und Morphologie des Limulus Polyphemus " (' Jenaischen Zeitschrift,' Bd. VI, 

 Heft 4, 1871, p. 639. 



8 "On the Development of Limulus Polyphemus," 'Mem. Boston Soc. of Nat. Hist.,' 1870, vol. ii, 

 p. 156. 



