PROFESSOR OWEN ON LIMULUS POLYPHEMUS. 203 



side, corresponding in the main in number with the apodemal spaces and the epimeral 

 nerves. The least unsuccessful trials of injecting the terminal canals and acini indicated 

 the greater transverse and less longitudinal extent of the hepatic lobes or primary 

 divisions of the gland. The gathering tubes of the initial or acinal ducts of these lobes 

 course, in the main, transversely towards the intestine until they quit the lobe, when 

 they converge abruptly to form the terminal duct. The anterior of these receives the 

 tributary ducts of the four chief anterior divisions of the liver ; the posterior terminal 

 duct is formed by the union of the same number. The ducts of two or three of the 

 anterior lobes unite to form that Avhich enters the main or terminal anterior duct ; those 

 from the four posterior lobes, unite and enter the posterior terminal duct by two canals. 

 The arrangement, however, may be varied in other specimens. But the principle of 

 segmental constitution as here exemplified will be found, I doubt not, in all Liiuuli. 

 It indicates the liver to have been developed in relation to the primitive composition of 

 the cephaletron, of seven or more antero-posteriorly succeeding segments, and that there 

 was a pair of livers or hepatic lobes to each. It interestingly exemplifies the way of 

 subsequent concentrative growth characteristic of the mature and procreative individual. 



" The bile is conducted to the intestines by two terminal ducts on each side ; the 

 first pair (fig. 2, PI. XXXIV /) open upon the sides of the beginning of the tube, where 

 it contracts to the ordinary calibre ; the second pair (ib., m) open about 9 lines beyond, 

 and nearer the dorsal part of the intestine. 



" As in the King-crabs, certain Spiders {Epe'ira, e. g.) have their ventral mouth 

 provided anteriorly with a chitinous plate, ' labrum ' or ' prostome,' and posteriorly with 

 a 'labium ' or ' metastome ' which is soldered to the cephaletral plastron, not bifid and 

 movable as in Limulus (Pis. XXXIV, and XXXV, fig. 1, *). The oesophagus rises, at 

 first, vertically dorsad, then bends back at a right angle, traversing in that part of its 

 course the neural ring before expanding into the stomach. This cavity is, in most Spiders, 

 produced into csecal appendages, which, in some, extend into the basal joint of the 

 cephalateral limbs. The bile-ducts open into that part of the intestine which traverses 

 the thoracetron (' abdomen ' of arachnologists). The proportion of difference to resem- 

 blance must be kept in mind when speculating on the degree of affinity of Xiphosura 

 to Arachnida." 



§ 4. "Sanguiferous System. — The dissection of Limulus was commenced from that aspect 

 or plane of the body next to which, in Invertebrates, is the part of the neural axis called 

 ' supercesophageal/ and which, as it supplies nerves to the organs of sense, answers to 

 the brain in Fishes. As in these Vertebrates also, the removal of the neural or dorsal 

 part of the skeleton exposes the vascular system analogous to the so-called ' aorta ' of 

 Fishes, and homologous with the ' dorsal vessel ' in Insects. In Limulus the walls of 

 this vasiform heart exhibit muscular and valvular structures, for the same purpose or 

 office as those of the vertebrate ' heart.' 



" In a specimen dissected, with a carapace, or upper crust of the two chief parts of 



