NERVOUS SYSTEM "OF INVERTEBRATA. 489 



function, entirely depend upon the number and variety of the organs to 

 be supplied. In the lowest Mollusca, the regulation of the ingress and 

 egress of water seems almost the only function to be performed ; and 

 here we have but a single ganglion. In the Star-fish, we have five or 

 more ganglia; but they are all repetitions one of another, and are ob 

 viously the centres of action to the several segments to which they 

 respectively belong, neither having a predominance over the rest. And 

 in the higher Mollusca, and in Articulata, we have a ganglion, or more 

 commonly a pair of ganglia, situated at the anterior extremity of the 

 body, connected with the organs of special sensation, and evidently ex- 

 erting a dominant influence over the rest. In the lower Mollusca, we 

 have but a single ganglion for general locomotion ; but this is doubled 

 laterally, and repeated longitudinally in ijie Articulata, in accordance 

 with the multiplication of their locomotive organs, so as to form the 

 ventral cord. In like manner, the Mollusca possess a single ganglionic 

 centre for the respiratory movements ; and this is repeated in every 

 segment of the Articulata, forming a chain of respiratory ganglia, which 

 regulates the actions of the extensively-diffused respiratory apparatus of 

 these animals. The acts of mastication and deglutition, again, in both 

 sub-kingdoms, are immediately dependent upon a distinct set of gan- 

 glionic centres ; which are connected, however, like the preceding, with 

 the cephalic ganglia. And we have further seen, that, wherever special 

 organs are developed, whose operations depend upon muscular contrac- 

 tion, ganglionic centres are developed in immediate relation with them ; 

 so as to enable them to act by their simple reflex power, as well as 

 under the direction of the cephalic ganglia ; as in the case of the suckers 

 of the Cuttle-fish. Now when we inquire into the relation of the 

 cephalic ganglia of Invertebrata with the Brain of the higher Verte- 

 brated animals, we find that these organs cannot be compared in their 

 totality ; for that the former are the representatives of a certain portion 

 only, and that usually but a small one, of the latter. The cephalic 

 ganglia of the Centipede, for example, receive nerve-trunks from the 

 eyes, the antennae, and other sensory organs, and give off motor nerves 

 to the different moveable parts of the head ; and the history of their 

 development, which has been studied by Mr. Newport, shows that they 

 may be considered as the coalesced ganglia of the four segments of 

 which the anterior part of the head is composed ; whilst the first sub- 

 oesophageal ganglia are formed by the coalescence of the four segments 

 entering into the composition of the posterior part of the head. The 

 increased bulk of the cephalic ganglia in the higher Articulata, and 

 especially in the perfect Insect, is obviously for the most part dependent 

 upon the increased development of the visual apparatus, for we find it 

 everywhere proportional to it ; and thus we may look upon them as 

 mainly optic ganglia, serving to direct the actions of the animal through 

 the sense of sight. There is no part of these organs which can be con- 

 sidered as superadded to the ganglionic masses which are the immediate 

 centres of the cephalic nerves ; consequently there is nothing which 

 can be likened either to the Cerebrum or to the Cerebellum of Verte- 

 brata. And the representative of these cephalic ganglia in the Verte- 

 brated Encephalon, is that series of ganglionic centres at the base of 



