DISEASES OF CATTLE 349 



The Worms are invertebrates with a soft contractile body, 

 nonarticulated or markedly divided into a number of transverse 

 rings. They are always destitute of limbs and usually inhabit the 

 hollow organs of the body, although the larval stage of different 

 species may be found in almost all of the tissues of the body. This 

 section contains a vast group, only one of which is of special im- 

 portance from a parasitical standpoint. These are the Helminths, 

 designated in many works as Entozoa, intestinal worms, etc., al- 

 though found in various organs. They are divided into two classes : 

 Plathelminths, with bodies usually flat, and Nemathelminths, with 

 bodies, usually cylindrical. The platheminths are nearly all her- 

 maphrodites, i. e., the male and female organs being present in the 

 same individual, and comprise three orders, viz: Cestodes, Trema- 

 todes, and Turbellaries, the first two of which furnish a large num- 

 ber of parasites to man and the lower animals. 



The cestodes are represented by the numerous species of tape- 

 worms. Their bodies are flat, ribbon-shaped and nude in the adult 

 form, segmented and provided at one extremity with organs of 

 fixation in the form of suckers or hooks. They have no digestive 

 apparatus, and in the adult form live in the intestinal canal of ani- 

 mals and man. In the larval form, however, they pass through cer- 

 tain transformations and migrate to organs very remote from the 

 intestinal tract, and in different hosts. 



The trematodes are represented by the various species of flukes, 

 one of which causes the so-called liver-rot of sheep. Their bodies 

 are soft, nude, and non-segmented and furnished with one or more 

 suckers. They have a digastive canal with but one opening that 

 of the mouth. Those which act as parasites live in the interior of 

 the body and are characterized by having not more than two suck- 

 ers, of which the anterior is oral. The turbellaries furnish no para- 

 sites, so need not be discussed here. The nemathelminths are 

 round worms in which the sexes are nearly always separate. They 

 comprise two orders, Aoanthocephali and Nematodes. 



The acanthocephali have no digestive canal and have a pro- 

 tractile proboscis armed with hooks. Only one species is found as 

 a parasite the Echinorhynchus, which, in the adult stage, lives 

 in the intestines. The nematodes, as a rule, have a complete diges- 

 tive canal with two openings. They are elongated, slender worms 

 and inhabit all the organs of the body except the bones and nervous 

 system. They furnish a large number of species, some of which 

 give rise to serious trouble and cause the loss of many animals. 



The arthropodes are invertebrates, always provided with artic- 

 ulate limbs. They comprise four classes, only two of which con- 

 tain species which are parasitic in the domestic animals, viz : Arach- 

 nidse and Insects. 



The Arachnidae are air breathing arthropodes. The head is usu- 

 ally fixed to the thorax ; there are two pairs of masticatory appendages, 

 fours pairs of feet, no wings and an appdous abdomen. They are 

 divided into ten orders, only two of which furnish parasites to the 

 warm blooded animals the Linguatulidse and the Acari. The 



