File:The causes and course of organic evolution; (1918) (14587360658).jpg

Identifier: causescourseofor00macf (find matches)
Title: The causes and course of organic evolution;
Year: 1918 (1910s)
Authors: Macfarlane, John Muirhead, 1855-1943
Subjects: Evolution
Publisher: New York, The Macmillan Company
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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ves of a bilobed cord,in which the connecting fibers remained as a bridge betweenthe more or less united halves; (5) receptor currents to, aswell as motor and inhibitory currents from, the cephalic gang-lia would increasingly traverse this bilobed cord, which wouldthus increasingly distribute the motor and inhibitory impulsesthroughout the body; (6) some rudiment might be left of thedorsal nemertean nerve, which starts from the dorsal com-missure that joins the olfacto-optic areas of the dorsal ganglia,and running backward distributes to the skin muscles accord-ing to Burger (p. 108). All of the above conditions are fulfilled in Petromyzon, inthe Apoda, and upward through higher types in increasinglyperfected manner as one rises throughout the series. In thisprocess the areas between the ganglionic masses become thebrain ventricles, or the iter connections between these.But a remarkable confirmation of the writers position, aswell as of the earlier views of Hubrecht and of Harting, is
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Fig. 18—a dorsal, 6 ventral view, brain of Ewpolia Giardii (afterHubrecht); c, d, of hypothetical protochordate type; e, f, of cyclos-tome type; ol. n., ol. a., rh., olfactory nerves and area or rhinencepha-lon; op. 71., op. a., optic nerves (which should be yellow in all) and area;th., the last evolved as thalamencephalon; p. c, posterior commissure;(i.?i., dorsal nerve becoming Reissners fibre in c-f; v. c, ventral com-missure; n:e., mid lobe or mesencephalon; n. s., auditory sac; ??i. y,ventral ganglia becoming myelencephalon or medulla in c-f; In, lateralnerves becoming sp. c. or spinal cord in c-f. Evolution of Animals 437 got under the sixth caption, and this in the following manner.In connection with captions 2 and 4, as gradual appositionand more or less perfect union of the ganglionic or brain massesand nerve cords took place, one of three fates might alsohave happened to the median dorsal nerve. Either it mighthave risen above the apposing masses to occupy a free positiond

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