DIPTERA. 791 



are chiefly those of the shoulder, base of the neck, and inner 

 part of the fore legs, especially about the knees ; for in these 

 situations the horse will have no difficulty in reaching the ova 

 with its tongue. When from any cause the animal licks those 

 parts of the coat where the eggs have been placed, the moisture 

 of the tongue, aided by warmth, hatches the ova, and in some- 

 thing less than three weeks from the time of the deposition of 

 the eggs, the larvse thus make their escape. As maggots, they 

 are next transferred to the mouth, and ultimately to tlie stomach 

 of the equine bearer along with food and drink. Of course a 

 great many larvoe 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 tlie many hundreds of eggs deposited on a 

 single horse, scarcely one out of fifty of their contained larvse 

 arrive within the stomach. ISTotwithstanding this waste, we are 

 all of us familiar with the circumstance that the interior of an 

 animal's stomach may become completely covered with the 

 larvse in the condition of " bots." Whether few or many, 

 they are retained in this singular abode chiefly by means of 

 two large cephalic hooks, which are inserted into the mucous 

 membrane. 



As soon as the bots have attained their perfect growth, as 

 such, they voluntarily loosen their hold, and allow themselves 

 to be carried along the alimentary canal until at length they 

 make their escape with the fseces. It is said that during their 

 passage through the intestinal canal they not unfrequently re- 

 attach themselves to the mucous membrane, thereby occasioning 

 severe intestinal irritation. When thus lodged in the neighbour- 

 hood of the anus they seriously inconvenience the animal. In 

 all cases, however, they sooner or later fall to the ground. 

 When once transferred to the soil they bury themselves beneath 

 the surface in order to undergo the change whereby they are 

 transformed from the bot state into the pupa condition. At 

 length, having remained in the soil for a period of six or seven 

 weeks, they finally emerge from their pupal envelope or cocoon 

 in the active life-phase of the imago or perfect dipterous insect. 

 It thus appears that these creatures in the form of bots ordinarily 

 pass about eight months of their lifetime in the digestive organs 

 of the horse. 



