YO NERVOUS SYSTEM. 



Dr. Lockwood, in the paper reported above, has witnessed a 

 similar movement by this species. 



NERVOUS SYSTEM. 



{Plate V.) This consists of a group of symmetrical ganglia 

 surrounding the oesophagus, communicating by commissures and 

 sending forth nerves to the various organs. This nervous collar 

 may be considered the representative of the brain of vertebrates. 

 It may be doubted whether the movements of the animal are 

 governed by will to any great extent, most of them appearing to 

 be the reflection of external stimulants, or automatic. The 

 ganglia and the nerves to which they give rise are speci^ized as 

 follows: 1 , cerebral ganglia ; 2, the asymmetrical ventral ganglia, 

 branchial, and visceral; 3, the symmetrical or paired pedal 

 ganglia ; 4, one or several pairs of small ganglia, called stomato- 

 gastric, and connected with the pharj^nx and oesophagus. 



The development of these several ganglia agrees with that of 

 the organs which they serve, and of course where an organ is 

 suppressed, as the foot in the attached oyster, the corresponding 

 ganglia are also undeveloped. Difference in the form of the 

 animals influences also the distribution of the nervous centres, 

 and is mainly shown in the length of the commissure or con- 

 nectives, which in some cases are very long, in others again, 

 quite short. 



The nerves of feeling or sensation are very widely diffused 

 throughout the body. The nerves by which motion is produced 

 are quite distinct from these, yet accompany them so closely as 

 to appear like parts of the same cords. 



Cephalopoda (v, 65, 66). The Nervous System is mainly 

 identical with that of the gastropods, yet the relatively high 

 position of the class is shown by the greater concentration of its 

 elements : in the Octopus the cerebral volume is considerable. 

 The cranial cartilage contains a pellucid fluid comparable to the 

 cerebro-spinal liquid of the vertebrates. There are the three 

 tjqDical pairs of ganglia, the cerebral, pedal and visceral, surround- 

 ing the gullet and connected by commissures ; whilst the nerves 

 which supply the buccal mass, the alimentary canal, the heart, 

 the branchiae and the mantle develop additional local ganglia.* 



* The change of color of cephalopods by the chromatophores (iv, 60, 61) 

 is a case of mimicry, but depends on the pallial nerves ; their section 

 paralyzes the dilator muscles of the cliromatophores and renders the 

 animal pale ; irritation darkens its colors by expansion of the same ; 

 intense light paralyzes them also temporarily. 



The nervous string in each arm of the cephalopods is a centre for reflex 

 movements, in the same manner as the spinal marrow in the vertebrata, 

 and these movements show the character of protection and defense, like 

 the movements of a decapitated frog. — Fredericq, Archw. Zool. Uxp., 

 vii, 535, Physiology of Octopus vulgaris. 



