INVEETEBEATA. 



FN one of the most complicated of invertebrate animals, as the lobster, the brain is 



small, when compared with that of fishes ; it gives off the optic nerves, nerves to 



the feelers, the organ of hearing and contiguous parts, and sends a long nerve on each 



side of the oesophagus, to give filaments to the stomach, and then join the first or 



suboesophageal ganglion, which sends branches to the mouth and adjoining parts. 



From the first ganglion the cord passes down to the next, and so on to succeeding 



ones as far as the tail ; filaments are given off to the branchiae, the muscles and 



integuments, and one passes to each extremity. The large artery supplying the 



extremities passes between the two halves of the cord just a above the ganglion, giving 



off the nerves to the last pair of legs. The ganglia become smaller below those which 



have supplied the extremities. Nerves issue both from the ganglia and cord to 



contiguous parts ; and the distinction between those passing from the dorsal or ventral 



surface is not clear. The nerves of the legs issue from the ventral surface. The 



posterior or dorsal layers do not send distinct fibrils to join the nerves issuing from 



the anterior or ventral, and the anterior do not send off branches forming distinct and 



separate ganglia in the same manner as the posterior origins in most of the vertebrate 



animals, but the ganglia are concentrated in the cord. There are more distinct and 



continued parallel lines on the dorsal surface than on the ventral. In another form, 



in which the body is more uniform throughout, as in the centipede, the brain gives 



branches to the feelers and eyes, and then sends a nerve on each side of the 



ossophagus to the ganglia beneath this ; lower down the nervous system consists of a 



B 



