. A manual of zoology. . sect, ix PHYLUM ANNULATA 205 with what we have met with in the Chaetopoda, and is to be looked upon as a mark of higher differentiation. The alimentary organs are greatly modified in accordance with the blood-sucking habits of the animal. Surrounding the mouth are three jaws, one median and dorsal, the other two ventro - lateral. Each has the form of a com- pressed muscular cushion, with a sharp, evenly curved, free edge covered with chi- tin, which is produced into numerous serrations or teeth (Fig. 118). By means of its CI Jy muscles each jaw can be 1 v 1 j r Fig. 11
. A manual of zoology. . sect, ix PHYLUM ANNULATA 205 with what we have met with in the Chaetopoda, and is to be looked upon as a mark of higher differentiation. The alimentary organs are greatly modified in accordance with the blood-sucking habits of the animal. Surrounding the mouth are three jaws, one median and dorsal, the other two ventro - lateral. Each has the form of a com- pressed muscular cushion, with a sharp, evenly curved, free edge covered with chi- tin, which is produced into numerous serrations or teeth (Fig. 118). By means of its CI Jy muscles each jaw can be 1 v 1 j r Fig. 118. â a, Head of Hirudo medici- moved backwards or for- naiis, showing the three jaws<k)-. a, Ac- fk ^ V. ^^ f â one of the jaws isolated, with the finely WarClS inrOUgn a Certain arc, toothed free edge. (After Sedgwick.) and the three, acting to- gether, produce the characteristic triradiate bite in the skin of the animal upon which the leech preys. The mouth leads into a muscular pharynx (Fig. 119,ph), situated in the fourth to seventh segments. Radiating muscles pass from its walls to the integument, and by their contraction dilate its cavity and suck in blood made by the jaws. Around the pharynx are numerous unicellular sali- vary glands, which open close to the mouth ; their se- cretion has the effect of preventing the coagulation of the blood taken as food. The pharynx communicates by a very small aperture with the second and largest division of the enteric canal, the huge crop (cr), a thin-walled tube extending from the eighth to the eighteenth segment, and produced into eleven pairs of lateral pouches (cr, cr. 1, 11). The crop is capable of great. 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
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