386 PARASITES OF ANIMALS 



escape. As maggots they are next transferred to the mouth, 

 and ultimately to the stomach along with food and drink. A 

 great many larvae perish during this passive mode of immigra- 

 tion, some being dropped from the mouth, and others being 

 crushed in the fodder during mastication. It has been calcu- 

 lated that out of the many hundreds of eggs deposited on a 

 single horse, scarcely one out of fifty of the larvae arrive within 

 the stomach. Notwithstanding this waste the interior of the 

 stomach may become completely covered with " bots." Whether 

 there be few or many, they are anchored in this situation chiefly 

 by means of two large cephalic hooks. After the bots have 

 attained perfect growth they voluntarily loosen their hold, and 

 allow themselves to be carried along the alimentary canal until 

 they escape with the faeces. Many persons suppose that during 

 their passage through the intestinal canal they re-attach 

 themselves to the mucous membrane, thereby occasioning severe 

 intestinal irritation. This is an error. In all cases they sooner 

 or later fall to the ground, and when transferred to the soil 

 they bury themselves beneath the surface, in order to undergo 

 transformation into the pupa condition. Having remained in 

 the earth for a period of six or seven weeks they finally emerge 

 from their pupal-cocoons as perfect dipterous insects. It 

 thus appears that bots ordinarily pass about eight months of 

 their lifetime in the digestive organs of the horse. 



That they are capable of giving rise to severe disease there 

 can be no doubt, but it is not often that the disorder is 

 correctly diagnosed, since it is only by the passage of the 

 larvae that the practitioner can be made aware of their presence. 

 Mr J. S. Wood has published a case of tetanus in a mare, 

 associated with the larvae of (Estrus equi, and Mr J. T. Brewer 

 has also given a case where the duodenum was perforated by 

 bots. Mr Goodworth records an instance of pyloric obstruction 

 from the same cause, and Mr W. Coupe informed me in 187G 

 that he had a drove of foreign ponies under his care, all of 

 which suffered irritation from haemorrhoidal bots. He removed 

 them with a pair of forceps. Although frequently said to do so, 

 the common bot does not attach itself to the rectum before finally 

 escaping the host. The larvae of G. hamorrhoidalis normally 

 reside there. In this situation they seriously inconvenience the 

 bearer. The bots of G. nasalis are often confounded with those 

 which ordinarily occupy the stomach of the bearer. The larvae of 

 G. nasalis commonly reside in the duodenum near the pylorus. 



