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: CHAPTER VI EXPERIMENTS ON WORMS 1. We shall consider separately in this chapter two kinds of worms: first, those in which the ganglia are all crowded together in the head end ? e. g., Planarians ; and second, those with a series of segmental ganglia ? e. g., Annelids. Sea- and fresh - water Planarians differ little
...structurally, yet they may show different reactions upon losing the oral ganglion. Thysanozoon (Broc- chii), Fig. 20, a marine Fig. 20. Thysanozoon Brocchii, A ri ' ytAR,NE Planarjan. Plananan, 1s very com mon in the Bay of Naples. It is from 1 to 3 cm. long and nearly as broad. The oral end of the body, which can be recognised by two tentacles Marine Planarian. g brain ; m, mouth; , longitudinal nerve. (Diagrammatic after Lang.) - 2O), contains the brain of the animal. This consists of two connected ganglia, from which a series of nerves, containing single ganglion-cells, go out ; among the latter, the two large longitudinal nerves running lengthwise throughout the animal (n, Fig. 20) are conspicuous. In the periphery a plexus is formed (1). The central nervous system consists of the double ganglion in the forward end. Like all Planarians, Thysanozoon crawls on the side of the aquarium or on the surface film of the water. It differs from the fresh - water Planarians in being able to perform, in addition, genuine swimming movements. With the sides of its body it makes vibrations similar to those made by the wings of a butterfly. If while a Thysanozoon is gliding about on the surface of the water it be divided transversely with a pair of scissors, the posterior or aboral half (6, Fig. 21) at once falls to the bottom, while the oral piece (a, Fig. 21) containing the brain creeps on undisturbed. If the division be made with asharp knife w... --This text refers to an alternate Paperback edition.
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