780 PERISTOMIAL HAEMOCOEL ; SYSTEMIC AORTA ; CEPHALIC ARTERIES. 



were continued uninterruptedly from one side to the other. Kerr has further found 

 a spermatophore adherent to the lamellae of this organ, thus indicating its function as 

 a receptaculum seminis. Curiously enough I have not found a spermatophore in this 

 position in any of my preserved females, but in a living female I once observed the 

 end of a spermatophore protruding from the circumoral complex as shown in fig. 2, 

 PL LXXVII. I placed this specimen carefully back into its cage, in the hope of obtaining 

 some result, but nothing came of it. 



On Plate LXXX. figs. 9 — 12, I have rendered all the secondary sexual characters 

 of a young female, measuring 66 mm. in length from the root of the siphuncle to the 

 anterior border of the hood. The organ of Valenciennes is mapped out but barely laid 

 down, although faint traces of the future lamellae are discernible at the sides. The 

 extrabuccal lobes (PL LXXX. fig. 10) exhibit normal development, since they are not 

 specially modified in the female, whereas the infrabuccal lobe shows a retarded develop- 

 ment, small in size and with the tentacles just appearing (fig. 11). In conclusion it 

 may be noted, although not coming within the scope of the present chapter, that the 

 nidamental gland is only represented by an inconspicuous primordial tract on the inner 

 surface of the ventral mantle-flap (PL LXXX. fig. 12). 



10. Peristomial Haemocoel; Systemic Aorta; Cephalic Arteries. 



The venous system of Nautilus consists of definite venous channels, of which the 

 most conspicuous are the vena cava, the pallial veins and the siphuncular vein, of inter- 

 stitial lacunae and of spacious sinuses. The sinuses are traversed by muscles, nerves, 

 and conjunctive trabeculae, and form vast cisternae, surrounding the buccal cone, the 

 crop, and the liver. These three principal divisions of the haemocoel may be distinguished 

 as the peristomial, peri-oesophageal and peri-hepatic haemocoels respectively. They com- 

 municate by separate apertures with the vena cava, which collects all the blood and 

 transmits it through the central sinus venoms and afferent branchial vessels to the gills. 



The peri-oesophageal haemocoel communicates with the vena cava by means of the 

 numerous fenestrations in the dorsal wall of the latter which were described and figured 

 by Owen (cf. my PL LXXXI. fig. 5). 



In preserved specimens the liver is often surrounded by an abundant coagulum which 

 conceals the hepatic lobules from view. The wall which shuts off the peri-hepatic sinus 

 from the perivisceral coelom is a thin transparent membrane. The liver, as is well known, 

 consists of right and left portions, and the peri-hepatic haemocoel accordingly opens into 

 the sinus venosus by two orifices which lie mediad of the posterior afferent branchial 

 trunk (which supplies the smaller gill on each side), and dorsad of the genital duct 

 on the right side, and of the pyriform body on the left. These orifices are seen at 

 the back of the sinus venosus after cutting across the rectum which traverses the latter. 



The peri-hepatic haemocoel is nevertheless nothing more than a backward prolongation 

 of the peri-oesophageal coelom, protruding like a hernia into the perivisceral coelom. That 

 this is the case may be seen at once by cutting into the haemocoel from the dorsal 



