. A text-book of invertebrate morphology. Invertebrates. TYPE PLATyHMLMINTHES. 137 The nervous system consists of a bilobed brain lying in the anterior part of the body and from wliich two nerve-cords pass backwards, united at intervals by cross-commissures and giving off on their outer sides branches which anastomose with one an- other, forming a network. In Qunda seginentata the transverse commissures agree in number and ar- rangement with the lateral branches on the one hand and with the diverticula of the intestine on the other, the arrange- ment of the two systems producing an appearance
. A text-book of invertebrate morphology. Invertebrates. TYPE PLATyHMLMINTHES. 137 The nervous system consists of a bilobed brain lying in the anterior part of the body and from wliich two nerve-cords pass backwards, united at intervals by cross-commissures and giving off on their outer sides branches which anastomose with one an- other, forming a network. In Qunda seginentata the transverse commissures agree in number and ar- rangement with the lateral branches on the one hand and with the diverticula of the intestine on the other, the arrange- ment of the two systems producing an appearance of metamerization which is most striking, especially as it affects as well the excretory and reproductive sys- tems. In this form an indication is afforded of the manner in which the more pronounced and typical metameri- zation of the higher types has been pro- duced by the more or less completed g multiplication of the organs and the integration of the parts so formed into a metamere (see p. 48). Byes are usually present, fre- quently provided with lenses, and, though usually two in number, may be very numerous and situ- Pig. 73.—A Teiclad Turbbllari- ated along the margin of the body. '^'^' Sy^l^^«^ pellucidi^m (after No otocysts occur, and the sides of the anterior end of the body are in some forms produced into more or less elongated processes which may possibly be mainly sensory in function, while behind them are areas of strongly ciliated cells richly supplied with nerves and presumably corresponding with the ciliated depressions oc- curring in the same region in the Alloiocoela and Wheeler). ex = excretory system. g = accessory gland. ggl = vaginal glands. n = nervous system. od = oviduct. ov = ovary. p = reproductive orifice. ph = pharynx. t = testis. u = uterus. vd = vas deferens. vi = Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of th
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