TOPOGEAPHICAL EELA.TIONS AMONG THE DOCOGLOSSA. 271 



corresponding more closely to those of the Prostreptoneure. There were certainly one 

 pair of buccal glands and probably a pair of dorso-lateral pouches in the buccal cavity. 

 Farther back occurred valves, probably dorsal and ventral, and behind them a pair of 

 lateral oesophageal pouches opened into the gut-cavity. In this region the appearance 

 of the gut in transverse section would be that of a very wide cavity with a pair of dorsal 

 longitudinal infoldings and a median ventral infolding forking into two towards its free 

 edge (PI. 17. tig. 22 a). The oesophagus reached back (PI. 15. fig. 6) as far as the bend 

 of the U, and was followed by the stomach, the region in which the digestive secretions 

 were intimately mixed with the food. 



With the Stomach communicated the spiral caecum, the great digestive gland, and 

 probably a crystalline style-sac. 



The Digestive Gland in Cephalopods, i. e. pre-torsional forms, consists of a pair of 

 compact lobes; but the torsion must have considerably altered the disposition of such a 

 massive organ, which could not change its position without affecting the external form 

 of the animal. It was probably squeezed out during the torsion and development of the 

 visceral hump, so that it afterwards filled the interstices between the gut and the body- 

 wall. It is doubtful whether any trace of the original paired condition remained in the 

 Prostreptoneure. The ducts of the digestive gland opened into a groove in the stomach- 

 wall, and this groove was, as in Kaliotls, continued into the cavity of the spinal caecum. 

 This, and the fact that the ducts of the digestive gland in Cephalopoda open into 

 the spiral caecum direct, suggests that one function of that outgrowth is to provide 

 a temporary store when necessary for the copious secretion of the digestive gland. In 

 that case the loss of the caecuiu by the Docoglossa may be correlated with the huge 

 increase in length of the stomach (PI. 15. fig. 8), and the consequent improbability of 

 wastage of the secretion due to its flowing on too far in tlie intestine. 



A crystalline style-sac is well known an.ong Lamellibranchs ; it also occurs in Nautilus, 

 and Moore and Eandles have found it in various Architaenioglossa. It may therefore 

 have occurred in the Prostreptoneure. This structure must not be confounded with the 

 spiral caecum, as they occur together in various forms, as Moore and Randies have shown. 



A rectal gland may have been present. 



The Nervous System has been stvidied in such detail by Lacazc-Duthiers, Bouvier, 

 Haller, Woodward, Pelseneer, Thiele, and others that its probable primitive Gastropod 

 condition is in the main a matter of general knowledge and agreement. It is not 

 therefore necessary to describe it in detail here. 



Controversy has arisen more especially with regard to the innervation of the cpipodium 

 and the evolution of pleural centres. The first question seems to be practically settled 

 in favour of the view, advanced by Huxley, Pelseneer, and Haller, that the epipodium is 

 a pedal organ, and that the ventral ganglionic cords of Fleiwolomaria, IlaUotis, &g. are 

 to be called " Pedal Cords." On this point, however, Thiele maintains another opinion ; 

 but the matter does not directly concern the Docoglossa, and it can therefore be passed 

 over without further comment. 



The pleural centres were certainly imperfectly developed in the Prostreptoneure, and 

 the lateral portions of the circumoesophageal ring were divided into two connectives on 



38* 



