. Parasites and parasitosis of the domestic animals : the zooÌlogy and control of the animal parasites and the pathogenesis and treatment of parasitic diseases . Domestic animals. â â¢218 PARASITES OF THE ANIMALS a,iius the alimoiitan' canal is usually a uniform tube with little or no flexion. The nervous system consists of a nerve ring surrounding the esophagus, and of the nerves given off from this ring passing forward and I^ack, the largest of which are in the dorsal and ventral lines. Along the course of these nerves there are ganglionic cells, ])ut there is no massing to form tr
. Parasites and parasitosis of the domestic animals : the zooÌlogy and control of the animal parasites and the pathogenesis and treatment of parasitic diseases . Domestic animals. â â¢218 PARASITES OF THE ANIMALS a,iius the alimoiitan' canal is usually a uniform tube with little or no flexion. The nervous system consists of a nerve ring surrounding the esophagus, and of the nerves given off from this ring passing forward and I^ack, the largest of which are in the dorsal and ventral lines. Along the course of these nerves there are ganglionic cells, ])ut there is no massing to form true ganglia as occurs in the Annelida. The sexes are usually separate, hermaphroditic forms occurring among free-living species. In general, the females attain a distinctly greater length and thickness of the 1 )0(1}' than do the males, and in other respects thej^ can easily he distinguished. The males are usually provided with chitinous cojiulatorj' organs known as spicules. These are curved, spine-like structures which lie in a sheath close to the anus, and they can Ije protruded or retracted through the cloacal opening (Fig. 120). They are usually two in number, but there may be but one. The character of the spicules often serves as a guide in the estab- lishment of relationships of cer- tain groups. Surrounding the spicules there is, in some forms, a membraneous expansion which is referred to as the caudal bursa or pouch. This structure is best developed in the Strongylidse, where its varied characteristics furnish an aid in the recognition of species. The bursa is a clasp- ing organ used in copulation, while the spicules serve to direct the course of the semen. In the female there is a special genital opening,âthe vulva, located on the ventral anterior half of the body, or it may be to- ward the anus, its position varying according to species. The cylindrical bod}' is usually more or less distended with eggs, and frequently' the egg-packed uteri can be distinctly seen
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectdomesti, bookyear1920
