SECTIONAL TRANSACTIONS.— D. 367 



These centres are so arranged as to provide a system which is potentially 

 capable of performing the most complex feats of sensory discrimination, 

 learning and modifiable behaviour, fully justifying the impression of the 

 superficial observer that these animals show a high degree of ' intelligence.' 



Although we know very little of the physiological basis for such phenomena 

 yet we may say that they depend on the presence of (a) sensory centres in 

 which nerve impulses from various parts of a sensory surface, say the eye, 

 are able to interact, giving the possibility of the recognition of shape : the 

 Cephalopods possess such an apparatus in their large optic lobes ; (b) centres 

 in which impulses from various sensory systems converge and are correlated 

 to give an appropriate reaction ; (c) centres in which constant nervous activity 

 is maintained in definite patterns throughout the life of the animal by 

 self- re-exciting chains of nerve cells. This constant activity may provide 

 the basis for ' spontaneous ' activity in complex patterns and for the modi- 

 fication of these patterns by learning and experience. 



The supra-oesophageal ganglia of Cephalopods contain systems of both 

 types (b) and (c), since fibres from various afferent sources converge and play 

 upon common neurons which then activate the motor centres for the control 

 of swimming, seizing, biting, etc. These highest centres are contained in 

 the lobus verticalis, a structure which increases in relative size during 

 the post-larval life of the animals. 



The motor centres lie in the suboesophageal ganglia, which are best 

 considered as derived from ganglionated cords of the type found in Amphi- 

 neura and, already much shortened, in Nautilus. The three great groups 

 of muscles by means of which overt behaviour is produced are those of the 

 arms, for seizing, of the retractors and mantle for rapid movement by the 

 ejection of water, and of the fin for slow movements. The first two are 

 controlled by motor neurons of the pedal and brachial and the palliovisceral 

 ganglia respectively. Dominating these lowest motor centres there is in 

 Decapods a special higher motor centre, the lobus magnocellularis containing 

 giant cells whose processes pass into the pedal and palliovisceral ganglia 

 and produce the simultaneous contractions of the muscles of the tentacles, 

 retractors and mantle which are involved in the quick darts after the prey. 



The more gentle and subtle movements of the fins are produced by the 

 cells of a special lobe of the palliovisceral ganglion which is controlled by 

 a direct pathway from the cerebral centres. 



Mr. E. J. W. Barrington. — The structure and function of the digestive 

 system of Amphioxus (ii.o). 



Several types of secretory and ciliated cells are distinguishable in the 

 epithelium of the mid-gut diverticulum and hind-gut, and there is an 

 elaborate system of ciliary mechanisms for manipulating the food and 

 secretions. Digestive secretions are swept out of the diverticulum in a 

 ventral ciliated tract, and wound into the food-cord which is set into rotation 

 by the powerful ciliation of the ilio-colon ring ; secretions from the mid-gut 

 are also added to it. Particles of mixed food and secretion are broken off 

 from the rotating mass and distributed over the epithelium for absorption, 

 which takes place mainly in the hind-gut, the particles being driven along 

 this partly by the oblique beat of the cilia in the ilio-colon ring and partly by 

 a dorsal ciliated tract leading backward from the mid-gut. Some absorption 

 probably occurs also in the diverticulum and mid-gut, but much of the 

 scattered material in the latter region is returned to the main cord by a lateral 

 ciliated tract on the left wall. There is good evidence that absorption is 

 associated with the ingestion of solid material. 



