72 Agricultural Journal of Victoria. 



ANIMAL PARASITES. 



By A. A. Brown, M.B., B.S. 

 No. VII. 



Nematodes, or Round Worms. 



Having dealt in a general way with the tape or ribbon worms 

 possessing jointed bodies, and having pointed out some facts con- 

 nected with their life histories, we now turn to another great division 

 of animal parasites constituted by round worms whose bodies are 

 not jointed. The round worms, or nematodes, are particularly exten- 

 sive invaders of the bodies of animals and birds, as well as of our- 

 selves, and they may be found lodging in the cavities and in the tissues 

 of organs of their hosts. They vary much in size. Some may be only 

 a line or two in length, and others several inches long. Some are the 

 cause of the most formidable diseases that can possibly attack man ; 

 others, again, cause great mortality amongst the lower animals. 



The anatomical characters of the neinatodes present the same 

 general features thrt)uglioiit. The sexes are distinct. The female, as 

 a rule, is generally much larger than the male. The mouth is situated 

 at the anterior end, and has surrounding- it papillae, or little nipple-like 

 projections. The mouth is practically a sucker and it is by means of 

 the mouth and papillas that the worms fasten themselves on to the 

 mucous membranes lining the cavities'of the tubes or organs in which 

 they exist. The mouth leads into the intestine, which runs straight 

 through the body. There is a rudimentary nervous system present. 

 In the male worm the generative organs consist of a single coiled 

 tube, and in the female they are much convoluted, and very complex. 

 When impregnated, these organs occupy nearly the whole of the body 

 of the female worm. The eggs, when ripe, escape from the female 

 worm, which may be sojovirning in the lungs or intestines of its host, 

 and eventually gain the outside world with the waste products. 



Unless damp earth or water is reached by the eggs, they do not 

 generally undergo further development. If exposed in dry situations 

 to the heat of the sun, the life of the eggs is destroyed. Droughts 

 minimise, wet seasons favor, the invasions of animals by parasites.' 

 In water or damp earth, the eggs undergo a certain stage of develop- 

 ment, and, even perhaps before passing from the bodies of the hosts, 

 a certain stage of development may have been attained. Before any 

 further development can occur the embryos require to make their way 

 into the bodies of certain other creatures known as intermediary hosts, 

 where they will receive both nourishment and protection to escort them 

 a stage on their journey. The intermediary hosts for many of the 

 round worms are grubs, snails, caterpillars, gnats, flies, and molluscs. 



