. Zoology. Zoology. THE TRILOBITES. 97 under side a set of about one hundred respiratory leaves or plates, into wliicli the blood is sent from the heart, passing around the outer edge and returning around the inner edge. In order to examine the internal anatomy the student can readily with a knife cut the body into transverse sections, as in Figs. 12U, 121, and also divide it longitudinally so as to show the parts as in Fig. 133. The alimentary canal consists of an oesophagus, which rises directly over the mouth, a stomach lined with rows of large cliiti- nous teeth, with a large conical, stop
. Zoology. Zoology. THE TRILOBITES. 97 under side a set of about one hundred respiratory leaves or plates, into wliicli the blood is sent from the heart, passing around the outer edge and returning around the inner edge. In order to examine the internal anatomy the student can readily with a knife cut the body into transverse sections, as in Figs. 12U, 121, and also divide it longitudinally so as to show the parts as in Fig. 133. The alimentary canal consists of an oesophagus, which rises directly over the mouth, a stomach lined with rows of large cliiti- nous teeth, with a large conical, stopper-like valve projecting into the posterior end of the body; the intestine is straight, ending in the base of the abdominal spine. The liver is very voluminous, ramify- ing throughout llie cepljalolhorax. The nervous system is quite un- like tiiat of other Crustacea; the brain is situated on the floor of the body in tlie same plane as the rest of the system, and sends off two. Fig. 123.—Horseshoe Crab. Side view. pairs of nerves—a pair to each pair of ej^es. Tlie feet are all sup- plied with nerves from atliick nervous ring surrounding the oesoph- agus. The nerves to the six pairs of abdominal legs are sent off from tlie ventral cord. The eggs of tlie horseshoe crab are rather large, and laid in the sand between high and low water. Just before it hatches it strikingly resembles a trilobite. After leaving the egg (Fig. 12-i) it swims about on its back or burrows in the sand; at first it has no tail-spine, this growing out at successive moults. In casting its shell the latter splits open in front, so that during the process it appears as if spewing itself out. Specimens a foot long are probably several years old. Order 2. Trilobita.—The members of this group are all extinct. The body has a thick dense skin like that of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of t
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1897
