. Animal biology. Biology; Zoology; Physiology. THE INVERTEBRATE BODY 103 space running from one end of the animal to the other, but con- sists of a linear series of chambers through the center of which runs the alimentary canal. The limits of these chambers are in- dicated on the outside of the worm by a series of grooves which encircle the body wall. In short, the body is made up of a series of essentially similar units known as segments, and thus affords a simple example of segmentation, which is a characteristic ex- pressed in varying degrees in nearly all the higher animals. Many of the c
. Animal biology. Biology; Zoology; Physiology. THE INVERTEBRATE BODY 103 space running from one end of the animal to the other, but con- sists of a linear series of chambers through the center of which runs the alimentary canal. The limits of these chambers are in- dicated on the outside of the worm by a series of grooves which encircle the body wall. In short, the body is made up of a series of essentially similar units known as segments, and thus affords a simple example of segmentation, which is a characteristic ex- pressed in varying degrees in nearly all the higher animals. Many of the chief organs of the Earthworm are developed as outgrowths from the walls enclosing the coelom, so that it is in Dorsal blood vessel Chloragogen cells >^ Typhlosole^^^ ,J^% Intestine Longitudinal muscle Circular muscle Epidermis Cuticle Setae / Coelom Ventral vesse. y Setae Nephridium Nephrostome Nephridiopore Nerve cord' Subneural vessel Fig. 61. — Transverse section through the middle region of the body of an Earthworm. this cavity that we find, for example, the main organs devoted to circulation, excretion, coordination, and reproduction. Moreover, the organs are symmetrically arranged with respect to the long axis of the body which passes from mouth to anus. For instance, the chief blood vessels and the nerve cord lie in the long axis and extend from end to end, while the excretory and reproductive organs are disposed in pairs on either side of this axis. Thus there may be passed through the main axis a single plane which divides the body into symmetrical halves, each of which is a ' mirror image' of the other. The main axis, therefore, extends from the mouth (anterior end) to the anus (posterior end), and the plane. 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 Woodruff, Lorande Loss, 1879-1947. Ne
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