. Comparative anatomy and physiology. chap, xii.] NER vo us Svs TEM OF PER IP A rus. 401 The ventral nerve cords are widely separated from one another, but are connected together by a large number of commissures (co1), of which there are from nine to ten for each segment of the body. From the outer borders of the cords nerve fibres are given off to all parts of the body, the whole of which is consequently sur- rounded by the ner- vous system ; and we have here, therefore, what is essentially a plexiform arrange- ment, but one which has, so to speak, be- come regulated. A further advance is to
. Comparative anatomy and physiology. chap, xii.] NER vo us Svs TEM OF PER IP A rus. 401 The ventral nerve cords are widely separated from one another, but are connected together by a large number of commissures (co1), of which there are from nine to ten for each segment of the body. From the outer borders of the cords nerve fibres are given off to all parts of the body, the whole of which is consequently sur- rounded by the ner- vous system ; and we have here, therefore, what is essentially a plexiform arrange- ment, but one which has, so to speak, be- come regulated. A further advance is to be found in the fact, that while the cords are everywhere CO- Fig. 172.—Anterior portion of the central , T J ,. Nervous System of Peripaius, show- vered by ganglion in? the Anterior Cerebral Ganglia, Cells On their ventral witj *he.,J;ateral Nerve Cords con- nected with one another by numerous commissures (co). (After Balfour.). E, Eye ; atn, antennary nerve ; co i, first com- missure: or??, nerves for the mouth ; org, oral ganglion; pn, pedal nerves; ft/', first ganglionic enlargement for tlie pedal nerves. surface, the ganglia are more especially numerous at one point in every seg- ment of the bodv, n > where they form such an enlargement as that marked ' in Fig. 172. Proneomenia may be taken as the simplest type of A A—16. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bell, F. J. (Francis Jeffrey), 1855-1924. London, Cassell
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