PERISTOMIAL HAEMOCOEL ; SYSTEMIC AORTA; CEPHALIC ARTERIES. 783 



After giving off branches to the buccal mass and to the shell-muscle, the main 

 vessel on each side passes below the cerebral capsule, and follows the inner concave 

 border of the coronal (pedal) ganglion (PI. LXXXIII. fig. 28). Having arrived at the end 

 of the ganglionic swelling, at the point where the latter passes into the comparatively 

 slender pedal commissure, the vessel passes below or behind the ganglion, and then bends 

 sharply backwards and upwards, sending branches to the tentacles (PL LXXXII. fig. 5). 

 Although too much stress need not be laid upon the vagaries of blood-vessels, yet 

 I think that this recurrent course of the main tentacular arteries may be regarded as 

 an indication of an important transposition of parts or change of topography which has 

 taken place during the evolution of the nautiline plan of organisation. 



At the point of flexure of the tentacular artery on each side a large branch is given 

 off which traverses the cartilage and is distributed to the alae infundibuli. 



In the peristomial fundus there are symmetrically placed apertures leading into 

 various lacunae in the massive cephalopodiura ; there is one particularly large sinus 

 surrounding the lower portion of the spadix in the male (PL LXXXII. fig. 5). The 

 intrabulbar sinuses are of great complexity and I do not propose to analyse them. They 

 are all connected by more or less wide fontanelles with each other and with the 

 peristomial haemocoel. 



With regard to the stomatogastric nerves I have nothing to add to Mr Graham 

 Kerr's account, except that the nerves are more deep-seated than his description might 

 lead one to expect. They are below the sheet-like protractor muscle and below all the 

 retractors, and hence it is hardly apposite to speak of them as Ijing "just below the skin" 

 (PI. LXXXIII. fig. 29). 



The great peristomial haemocoel which is such a remarkable feature in the haemal 

 system of Nautilus communicates \vith the endochondral sinus by two channels which 

 lie between the dorsal protuberances (arcus cartilaginis) of the capito-pedal cartilage, 

 and the capsule of the pedal commissure (PL LXXXII. fig. 5). 



These are the most important fontanelles in the wall of the endochondral sinus, 

 and I propose to name them the capito-pedal venous orifices. I have seen a delicate 

 membranous fold on the iimer wall of the endochondral sinus arching over the orifice 

 as if it were a valve to prevent the reflux of blood from the sinus to the haemocoel. 

 These are the capito-pedal valves, but I cannot certify as to their constant occurrence or 

 effective function though I deem it worth while to direct attention to them (PL LXXXIII. 

 fig. 14). 



The blood of Nautilus when freshly dra-svn exudes as a colourless fluid which quickly 

 turns bluish at the edges of the fluid mass after exposure to the air, and the bluish 

 tinge gradually advances to the centre. When this has taken place the blood appears 

 of a uniform pale blue colour, which subsequently becomes darker. The blood does not 

 coagulate of itself if left to stand. It contains numerous amoebocytes, which I have 

 sometimes observed both in living and stained preparations to be united together in 

 small groups after the manner of a plasmodium, possibly the result of successive 

 nuclear divisions (PL LXXXIII. figg. 1 and 1 a). The nucleus of the amoebocytes presents 

 a chromatic network, while the protoplasm appears as a spongy reticulum, containing 

 granules which are dissolved by acetic acid. 



