﻿12 BRITISH FOSSIL CEPHALOPODA. 



the other end too ; but Keferstein represents it as opening into the mantle cavity. 

 It has a folded interior, but no office is assigned to it, though Prof. Owen suggests 

 it may be an aborted tube of communication between the venous and arterial 

 system. The ultimate distribution of the blood cannot be traced in the Nautilus. 

 On the one hand, if it be true, as Koffman asserts, 1 that in other Cephalopoda its 

 ultimate destination is into sinuses with definite walls, and not into general lacunae 

 between the viscera (and we remember that there is communication between the 

 pericardium and the exterior in the Nautilus), it would appear very unlikely that 

 blood and water should be thus mixed, but more probable that it should be retained 

 within walls : on the other hand, the peculiar structure of the vena cava would 

 appear useless in that case (fig. 2, a, b). The blood from the lower parts of the 

 animal is collected into a large sinus which is excavated in the body of the cartilage 

 and in its two lower horns ; from thence it passes backwards by a large vena cava, 

 which lies on the ventral side of the body, or upper side of the mantle cavity, between 

 the two shell-muscles, though it does not expand as the latter separate ; it is bounded 

 below by the membrane of the mantle cavity, but within it has transverse muscular 

 fibres lying upon it, which leave small apertures between them, by which its interior 

 is in communication with the visceral cavity : thus blood in that cavity, or sea-water 

 which might gain admission there, may equally well be introduced into the circula- 

 tion. When this vena cava has passed into the neighbourhood of the heart, other 

 veins from the viscera, including one from the liver, join it, and form a venous sinus 

 (fig. 2, c). From the sides of this sinus a vein arises on each side ; this quickly divides 

 into two, which become the afferent veins of the two branchiae (fig. 2, d). There are 

 no expansions of these veins, but some peculiar glandular follicles lie upon them, and 

 on the remoter sides (fig. 2, e) are closed sacs, while between them lies a space 

 which is part of the general visceral cavity, i.e. the pericardial portion of it. Into 

 each of the closed sacs (fig. 6, d°, d', d") there is an aperture from the mantle cavity 

 (fig. 6, e). The lower one opens on a little tubercle near the base of the lower 

 branchia, and the upper by a narrow slit near the base of the other branchia. Close 

 to this last aperture, and nearer to the middle line, is a third, larger, one leading 

 into the pericardial space, which it thus puts in communication with the exterior. 

 Valenciennes describes this as having an overhanging and so valvular edge, so 

 that it should serve for exit only. Between the bases of the two branchiae there is 

 also a small -tubercle of unknown use. In the two " excretion sacs " are a number 

 of follicles collected into two flattened plates by a superficial membrane, which as a 

 whole have a kidney-shaped appearance. The sacs are open at the distal end, and 

 also (according to Owen) at the junction with the vein (but, according to Keferstein, 

 they are closed). The inside of the sac is filled with concentric concretions of phos- 

 phate of lime, amongst which the follicles lie imbedded, but there is no uric acid, 



1 Zeitschrift fur Wiss. Zool. vol. xxvi. p. 87. 



