The brain as an organ of mind . s aregiven off on each side; v\^hilst a thirdpair issues from the cord itself, justanterior to the swelling, and is dis-tributed along the anterior boundariesof the segment. In Serpula, one of thesmall tube-dwelling marine worms, theventral ganglia are also very minute,and those of the two sides, togetherwith the ventral cords, lie some distanceapart, and are connected by a series of . ^ T . Fig. Sys- COmmiSSUreS (fig. 32, b). in this dlS- tem of Serimla cntortu- position of the great nervous cords we gSSXlfrX^l?- have something intermediate between
The brain as an organ of mind . s aregiven off on each side; v\^hilst a thirdpair issues from the cord itself, justanterior to the swelling, and is dis-tributed along the anterior boundariesof the segment. In Serpula, one of thesmall tube-dwelling marine worms, theventral ganglia are also very minute,and those of the two sides, togetherwith the ventral cords, lie some distanceapart, and are connected by a series of . ^ T . Fig. Sys- COmmiSSUreS (fig. 32, b). in this dlS- tem of Serimla cntortu- position of the great nervous cords we gSSXlfrX^l?- have something intermediate between phageai gangUa; 6, sub- their lateral position in the Nemerteans, ^/gangiSliated^cords ^n, and their contis^uous mid-ventral posi- motor buccal nerves; <,tac- ^ tile neives. tion in the Leech and the Earthworm. As in the latter, so m Serpula, the afferent nerves entering the brain {t) seem to be in the main tactile. The oesophageal ganglia in the Earthworm are, propor-tionately to the rest of the nervous system, much smaller. 92 THE NERVOUS SYSTEM OF VERMES. than in the Nemerteans ; and this is perhaps due in greatpart to the existence in it of the numerous segmentalganglia,—structures which are absent in the above-men-tioned marine worms. The movements of the Nemer-teans, Hke those of the Nematoids, are probably muchmore exclusively under the control of the oesophagealganglia than are those of the segmented Earthworm—inwhich each of the body ganglia, doubtless, has much to dowith bringing about the contraction of its contiguousmuscles in the same segment. The Earthworm has a more complex visceral structurethan is to be met with among the Nemerteans; and itpresents distinct evidences of a nervous interconnectionbetween its internal organs and some of the principalnerve-centres. Lockhart Clarke has described a complicatedgauglionic network on each side of the oesophagus, start-ing from the lateral commissures and sending prolonga-tions to the intestine and other parts. By
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Keywords: ., bookcentury1, booksubjectbrain, booksubjectpsychologycomparative
