. Elements of conchology / Prepared for the use of schools and colleges. Mollusks. NERVES OF MOLLUSKS. 11. Fig. 2. NERVES OF A JANTHINA. (a) are sometimes considerably separated from each other, and only united by an intermediate cord, and sometimes glued one to the other, or even confounded in a single mass: they are situate above the oesophagus, and far from the posterior ganglia (ft), which are placed beneath the intestine towards the posterior part of the body. In some mollusks, the nervous system is still more simple in its composition ; but, in "^, general, the ganglia tend to appro
. Elements of conchology / Prepared for the use of schools and colleges. Mollusks. NERVES OF MOLLUSKS. 11. Fig. 2. NERVES OF A JANTHINA. (a) are sometimes considerably separated from each other, and only united by an intermediate cord, and sometimes glued one to the other, or even confounded in a single mass: they are situate above the oesophagus, and far from the posterior ganglia (ft), which are placed beneath the intestine towards the posterior part of the body. In some mollusks, the nervous system is still more simple in its composition ; but, in "^, general, the ganglia tend to approximate the oesophagus more and more {fg. 2), and in most of these animals we find a greater num- ber of small medullary masses, some of which form a sort of nervous centre, and the others are distributed in different parts of the body. Thus, in the snails and most mollusks constructed on the same plan, and named gastero- pods (from the Greek, gaste?', belly, and pous, foot), on account of their mode of crawling on the ventral surface of the body, there g exists, above and in front of the p cesophagus, a medullary mass (fg. S, c), which is the representative d of the anterior pair of ganglia above mentioned,, and which is re- a garded by most anatomists as the Fig. 3.—nerves of a snail. generally called the brain ; here, these two ganglia are considerably sepa- rated from each other, and are united by a transverse band ;—c. nerves which arise anteriorly to be distributed to the tcntacula, to the mantle, &c.; —b. ventral pair of ganglia, which are united in a single mass, placed be- neath the intestine, and joined to the anterior ganglia by two very long nervous cords;—d. nerves which arise from the posterior ganglia to be dis- tributed to the mantle, &lc. Explanation of Fig. 2,—Nervous system of a Janthina ; a gasteropod mollusk, in which the posterior ganglia (h) as well as the anterior ganglia (a) are separated from each other ; but they arc more approximated
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectmollusks, bookyear184
