﻿BRITISH FOSSIL CEPHALOPODA. 13 



The glandular masses which open on the opposite side of the vein and hang into the 

 pericardial cavity consist each of a single tuft, which is larger than all the mass in 

 the excretion sacs. They are covered by a fatty substance, and have an exterior 

 layer of nucleated cells. Macdonald has minutely described the structure of one or 

 other of these follicles, but he did not distinguish between those in the sacs and 

 those in the pericardial cavity. The interior of those described by him is thrown 

 into folds radiating from the proximal end, and set with papillae, appearing like a 

 circular fan or folded filtering paper, forming an efferent valve. The function of 

 these appendages seems doubtful. From their position they might be thought renal, 

 yet they contain no uric acid. They may, however, be excretory in some way, and 

 the laminated ones may have a different function from the others. Prof. Owen 

 has suggested that they might act as reservoirs to relieve the pressure of the blood 

 during the animal's ascent to the surface. From the neighbourhood of these follicles 

 each afferent vein, after the junction of another from the shell-muscle of its side, 

 reaches the base of its own branchia, the entrance to which is narrow and valvular. 



The branchiae are four — two on each side — the anterior ones are smaller and 

 nearer to the median line ; each stands on its own separate pedicle, and lies free in 

 the branchial chamber, or mantle cavity. The larger branchia (fig. 6, c) is composed 

 of between forty and fifty transverse laminae, which are divided and subdivided into 

 filaments which collect again to lead to the efferent vein on the opposite side, and so 

 appear to be arranged alternately ; the efferent vein expands before leaving the 

 branchia and has orifices all along it (fig. 2,/). The efferent veins lie free from the 

 peritoneal investment and reach the heart without change. The smaller branchia 

 has about three-fourths as many laminae as the larger. 



There are folds of peritoneum crossing the visceral oavity from back to front 

 which more or less separate the posterior part with the heart from the venus sinus, 

 and several other organs, but leaving wide apertures by which one compartment 

 communicates with the other. Through the middle one of these passes the siphon 

 with its artery, which is thus put in communication with the exterior through the 

 pericardium. 



The central nervous system is partly protected in the cartilaginous groove 

 surrounding the oesophagus already described, and partly supported by a tough 

 membrane. It consists dorsally of a thick transverse commissure between the 

 great sense ganglia, and ventrally by two thick cords, joining the dorsal part at 

 the same points ; one of these is in front and slightly concave forwards, the other 

 behind and deeply concave forwards. From these three cords eleven sets of nerves 

 take their origin. From the front border of the first come off (1) the ocular, 

 from near the junction with the other cords ; (2) the nasal, just beyond ; (3) the 

 aural, from within the other two ; (4) super-oculo-tentacular,. from an origin nearer 

 the middle line and the sub-oculo-tentacular from behind. From the hinder border 



