Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 NERVOUS SYSTEM OF ARTHEOPODA. 253 In addition to the nerveSj set apart for the muscular system and tlie integument, there are also nerves for the viscera; of these the enteric nerves are most exactly known. They partly agree with the characters which obtain in the An- nelides. As separate ganglia are embedded in their course, they con- stitute to a certain extent an inde- pendent nervous system, which is called the ' stomato-gastric nervous system.' Another special system of nerves, which
Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 NERVOUS SYSTEM OF ARTHEOPODA. 253 In addition to the nerveSj set apart for the muscular system and tlie integument, there are also nerves for the viscera; of these the enteric nerves are most exactly known. They partly agree with the characters which obtain in the An- nelides. As separate ganglia are embedded in their course, they con- stitute to a certain extent an inde- pendent nervous system, which is called the ' stomato-gastric nervous system.' Another special system of nerves, which obtains especially in the Insecta, arises from the gan- glia of the ventral medulla, and is known as the sympathetic nervous system. § 196. The nervous system of the Crustacea presents us with a large number of examples of the phaj- nomena described in the foreo^oing; paragraph. The relation between the size of the cerebrum and the development of the optic organs is seen in the Thoracostraca, and in the large-eyed Hyperida (Phronima) among the Arthrostraca, where the optic nerves arise from distinct lobes ; these lobes are also distinct in the Wood-lice. The separation of the cerebral mass into various groups of ganglia generally implies a higher differentiation. With this ought to be compared those de- generations which affect the cere- brum when the optic organs are reduced or altogether lost; when this happens the antennae also gene- rally disappear. Conditions of this kind are found in the parasitic Cope- poda, and in the Cii'ripedia (Fig*. 129, B gs), and in consequence of it the cerebrum is sometimes repre- sented by nothing but a commissure. The most anterior of the ventral ganglia is connected to the cerebrum by a shorter or longer commissm'e. The length of this chord appears to depend on the position of the mouth with regard to the cerebral ganglia (that is really to the eyes and antennte). In the Malacostraca the length is very considerable (Fig. 128, c; Fig. 129, A)
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