Outlines of Comparative Anatomy And Medical Zoology

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: and traversing the body for this purpose, either through a water-vascular system (q. v.), or through a system of tracheal tubes, as in Myriapoda, Insecta, and certain Arachnida. Or the blood maybe brought to the medium, either through agency of (1) vascular processes (branchiae), or (2) lungs.?(1) When the former, they may be suspended in the water, as in Pisces, the aquatic Mollusca, most Annelida, Crustacea, all larval and a few adult forms of Batrachia; or be inverted, forming a branching tube, as in Holothuria (sea cucumber). (2) When the latter, special air sacs are developed, which may be simple pneumonic chambers, as in terrestrial Gasteropoda, and pul- monate Arachnida, or lobulated, generally symmetrical sacs, opening by tubes (bronchi) into a single passage (trachea), as in all air-breathing Vert