Guide to the study of insects and a treatise on those injurious and beneficial to crops, for the use of colleges, farm-schools, and agriculturists . n the Vertebrates,the nervous cord of insects iscomposed of two distinct columnsof fibres placed one upon the othercolumn, which is nearest to the exterior of the body, is that inwhich the ganglia, or enlargements, are situated. The upperone, or that which is internal and nearest to the viscera, isentirely without ganglia, and passes directly o\er the gangliaof the under column without forming part of them, but in \ery * Bennet on the Anatomy of t
Guide to the study of insects and a treatise on those injurious and beneficial to crops, for the use of colleges, farm-schools, and agriculturists . n the Vertebrates,the nervous cord of insects iscomposed of two distinct columnsof fibres placed one upon the othercolumn, which is nearest to the exterior of the body, is that inwhich the ganglia, or enlargements, are situated. The upperone, or that which is internal and nearest to the viscera, isentirely without ganglia, and passes directly o\er the gangliaof the under column without forming part of them, but in \ery * Bennet on the Anatomy of the Thorax in Insects, and its Function duringFlight. Zoological Journal, vol. i, p. 3i!4. tThe brain of insects is formed of several pairs of ganglia, correspondins,probably, to the number of primitive segments composing the head. The nervouscord is thus, in the head, massed together and compacted to form a brain. Fig. 43. Nervous System of CorijdoIns cornutus. «, cerebrum; b, cere-brellum; c, thoracic ganglia, which distribute a nerve to each leg; </, eight pairsOf abdominal ganglia. The dotted lines repnsent ilie wings.— F/om Fig. 43. The under or external 34 THE CLASS OF INSECTS. close approximation to them. Newport also believes that theganglionless upper, or internal, colnmn of fibres is analogousto the motor column of Vertebrata, while the external, or underone, corresponds to the sensitive column, thus representing thecerebro-spinal system of the Vertebrata. From each pair of ganglia are distributed special nerves tothe various organs. In the larva of Sx>liinx the normal num-ber of double ganglia is thirteen, and the nervous cord of theNeuroptera and other lowly organized and attenuated forms ofinsects corresponds in the main to this number. In the adultinsect, especially in the Coleoptera, Diptera, Lepidoptera, andHymenoptera, the tlu-ee thoracic ganglia are fused together,following the fusion and general headwise development of thesegments of the teg
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Keywords: ., bookcentury1800, bookdecade1880, bookpublishe, booksubjectinsects
