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the tumours called warbles. The fly is provided with an ovi-positor, Ij)- 

 means of which it bores holes through the skin, in each of which it deposits 

 one egg. The eggs develop into bots, which may be recognised b)' the 

 growth of little elevations or tumours, called warbles. The tail end of the 

 bot places itself in the tumour of the host, in order that it may be enabled to 

 breathe. The bot, when completely developed, escapes and buries itself in 

 the ground, and then passes through the chrysalis stage, in which it remains 

 about six weeks, at the end of which time it at length emerges as a perfect 

 fly, which again deposits eggs, and so the cycle goes on again. The eggs of 

 the bot-fly of the sheep are deposited in the nostrils, to the great distress of 

 the poor animal. The larvae or bots pass upwards towards the sinuses or 

 cavities of the forehead of the sheep, and thus cause great^distress. 



ASCARIS LUMBRICOIDES. 



A, Female Ascaris Lumbricoides. B, Anterior extremity enlarged, seen from tlie side>. 

 C, The same, seen from the front, showing the opening in the centre. 

 E, The Posterior extremity enlarged. D, Male Ascaris, natural size. 

 G 



