NATURAL HISTORY OF AMERICAN LOBSTER. 23 1 



appendicular and other nerves which spring from it, the lobster has certain stomato- 

 gastric nerves and ganglia which have been described as a rudimentary sympathetic 

 nervous system. 



The brain or compound supra-esophageal ganglion (pi. xxxiii) is united, by means of 

 a ring-commissure which embraces the esophagus, to the chain of paired ganglia; this 

 traverses the mid-ventral portion of the body and is protected by an archway of the 

 internal skeleton in the thorax. The brain, which is thus the only ganglionic part of the 

 central nervous system dorsal to the alimentary tract, appears as a small whitish mass 

 at the base of the rostrum and between the stalks of the compound eyes. It gives 

 origin to the following paired nerves: (o) The large optic nerves, which terminate in 

 the optic ganglia and the compound eyes of the eyestalks; (b) the antennular nerves 

 supplying the first pair of antennae, and (c) antennal nerves which innervate chiefly 

 the second pair of antenna. The brain thus represents the fused ganglia of the first 

 three somites and is connected by esophageal commissures with the central cord. 



The subesophageal ganglion, or first ventral link of the chain, lies below the 

 mouth and is composed of the ganglia of the mandibles, the maxilla, and the maxilli- 

 peds (segments iv-ix), more or less intimately fused together, the ganglia of the large 

 maxilUpeds being nearly or quite independent. 



Then follow five pairs of thoracic ganglia, which supply the legs and body wall, 

 and six abdominal ganglia, the last of which sends nerves into the terminal telson. 

 The longitudinal commissures between the twelfth and thirteenth somites diverge to 

 admit the sternal artery, which thereupon divides, one of its branches passing forward 

 and the other backward immediately under the nerve cord. (For nerves of cheliped, 

 see ch. vii, p. 265). 



In the embryo and larva the nervous system is much more concentrated than in 

 the adult, and according to Allen (2) the thoracic ganglia are fused into one mass, which 

 is united by short commissures to the brain. The hinder part of the embryonic brain 

 is connected by a bridge commissure, which in the adult lies immediately behind the 

 esophagus. 



The nervous system is composed of a central " Punkt-Substanz " or neuropUe, which, 

 though granular in appearance, is in reality a felt work of fibers running in aU directions, 

 and an outer covering of ganglion cells. According to Allen the posterior ganglia of 

 the chain give off two pairs of nerves, an anterior and posterior division; the anterior 

 nerve becomes a double branch in the adult lobster and supplies the limbs, while the 

 posterior division innervates the body wall. 



THE PERIPHERAL STOMATO-GASTRIC SYSTEM. 



In passing down the esophageal commissures, at a distance of about two-thirds of 

 their course from the brain, a small commissural ganglion is seen upon either side lying 

 against the wall of the esophagus. The delicate bridge commissure, which indirectly 

 unites both sides of the brain, lies immediately behind these small ganglia and toward 

 the lower side of the gullet, as already seen. Each commissural ganglion gives off two 



