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Show 18 HABITS OF WORMS. CHAP. I. latter organ 1s lined with a smooth thick Mouth. Pharynx. (Esophagus. Calciferous glands. <Esophagus. Orop. Gizzard. Upper part of intestine. Fig. 1. Diagram of the alimentary canal of an earthworm (Lumbricus), copied from Ray Lankester in ' Quart. Journ. of Microscop. Soc.' vol. xv. N.S. pl. vii. chitinous membrane, and is surrounded by weak longitudinal, but by powerful transverse muscles. Perrier saw these muscles in energetic action; and, as he remarks, the trituration of the food must be chiefly effected by this organ, for worms possess no JaWs or teeth of any kind. Grains of sand and small stones, from the -lo to a little more than the fo inch in diameter, may generally be found in their gizzards and intestines. As it is certain that worms swallow many little stones, independently of those swallowed while excavating their burrows, it is probable that they serve, like mill-stones, to triturate their food. The gizzard opens into the intestine, CHAP. I. THEIR SENSES. 19 which runs in a straight course to the vent at the posterior end of the body. The intestine presents a remarkable structure, the typhosolis, or, as the old anatomists called it an intestine within an intestine ; and Clapa-' rede * has shown ' that this consists of a deep longitudinal involution of the walls of the intestine, by which means an extensive absorbent surface is gained. The circulatory system is well developed. Worms breathe by their skin, as they do not possess any special respiratory organs. The two sexes are united in the same individual, but two individuals pair together. The nervous system is fairly well developed ; and the two almost confluent cerebral ganglia are situated very near to the anterior end of the body. Senses.-Worms are destitute of eyes, and at first I thought that they were quite insensible to light; for those kept in confinement were repeatedly observed by the aid of a candle, and others out of doors by the aid of a lantern, yet they were rarely alarmed, although extremely timid ani1nal ·. Other * Histolog. Untersuchungen i.ihcr die Regenwtirmer. 'Zcitscbrift flit· wissenschaft. Zoologic,' B. :xix., 18G9, p. Gll. c 2 |