The Anatomy and Physiology of the Blow-Fly, a Monograph
by Benjamin Thompson Lowne (9780217377577)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: Section IV.?The Nervous System. The nervous system, or rather, that part which is analogous to the cerebro-spinal system of vertebrates, is next to the integumentary in point of importance as far as regards type. Insects belong to that division of the animal kingdom which Professor Owen terms Homogangliata, that is, animals in which the nervous system is represented by a pair of nervous cords which traverse the ventral portion of the body, and lie next to the integument, uniting and fonning a ganglion for each segment, from which the proper nerves of the segment are given off. No insect that has yet been examined departs from this type so much as the fly and its allies; for, even in the larva state, the whole of the nervous system is collected in the anterior segments, and the pair of ventral cords do not exist; whilst, in the iinago, with the exception of two small ganglia in the proboscis, there are but two nerve centres, one situated in the head, and one in the thorax. The first of these, called the cephalic ganglion on account of its position, is the homologue, that is, the anatomical representative of the cosophageal ganglion or ring of the lower forms of life; it surrounds the oesophagus and gives off four pairs and one single nerve, which are distributed to every part of the insect's head. It is connected with the great thoracic nerve centre by a thick cord which represents the double ventral cord, typical of the insecta. The nerves given off from this ganglion, or more correctly speaking, collection of ganglia, for it is really composed of at least six, may be properly divided into two classes, those which consist entirely of nerve fibres having their origin in its substance, and those of which some of the nerve fibres at least, probably the greater portion, mere...

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