. A manual of zoology. 3°6 MANUAL OF ZOOLOGY the terminal part of the intestine close to the anal aperture is the duct of a peculiar gland — the ink gland (Fig. 193, 1). This secretes a black substance, the ink, which is discharged when the animal is irritated or alarmed, and mingling with the water in the mantle-cavity is discharged as a dark cloud, under cover of which the animal may elude the pursuit of an enemy. The heart and vascular system reaches a high stage of development. The heart consists of a median ventricle and frtCLnt Fig. 191. —Nautilus pompilius, interior of mantle-
. A manual of zoology. 3°6 MANUAL OF ZOOLOGY the terminal part of the intestine close to the anal aperture is the duct of a peculiar gland — the ink gland (Fig. 193, 1). This secretes a black substance, the ink, which is discharged when the animal is irritated or alarmed, and mingling with the water in the mantle-cavity is discharged as a dark cloud, under cover of which the animal may elude the pursuit of an enemy. The heart and vascular system reaches a high stage of development. The heart consists of a median ventricle and frtCLnt Fig. 191. —Nautilus pompilius, interior of mantle-cavity of a male specimen with the postero-ventral wall reflected, a. 1. neph. ap, oral left nephridial aperture: an, anus ; cten, ctenidia ; /. $ ap, left reproductive aperture ; /. ant. os, left oral osphradium ; / vise ap, left viscero-pericardial aperture ; mant, flaps of mantle : pen, penis; /. A neph. np, aboral left nephridial aperture ; /. r. neph. tip, aboral right nephridial aperture ; post, os, aboral osphradia ; ?-. vise, np, right viscero- pericardial aperture. two or four elongated lateral auricles or branchio-cardiac vessels conveying the blood from the ctenidia to the ventricle. The nervous system is highly developed, and its principal central parts, representing the cerebral, pedal, and visceral ganglia of other molluscs, with their commissures and con-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Haswell, William A. (William Aitcheson), 1854-1925. New York, The Macmillan Company; London, Macmillan & Co. ,Ltd.
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