23 



the hind legs. The fly was never seen to strike the calf on the back. 

 It works very quickly, but only for a few minutes at a time. H. 

 linealum lays its eggs on the hairs in rows and must therefore cling 

 on for a few minutes while laying them, but H. bovis lays its eggs 

 singly and quickly, greatly exciting the animals. It is believed that 

 the mere irritation caused by the fly touching the calf is enough to 

 cause gadding and terror, the animals do not seem to mind many 

 other flies, some of which are blood-sucking, such as species of Haema- 

 to pot a. Eggs were obtained by putting a captured fly " sleeved "_ in 

 a wire gauze cage on a calf's back or side, 60 eggs on one occasion being 

 laid in an hour. The eggs hatched on the fourth day and the first- 

 stage larva is described. The aspect of this larva suggests that it 

 could bore as readily through the skin as through the mucous mem- 

 brane of the gullet, and that it does so penetrate the skin seems to be 

 proved by the result of the muzzling experiments and of the obser- 

 vations recorded below. The results of the muzzling experiments 

 indicate no protection from warbles for those calves which cannot 

 lick themselves and confirm the opinion that the maggot usually enters 

 the host's body through the skin. The tongue, far from aiding the 

 parasite, rather inhibits its progress and fewer maggots are 

 found in animals that can lick themselves. A clothing experiment 

 showed that covering the back is no protection, but covering the legs 

 seems to be effectual. The result of an experiment in feeding calves 

 with eggs and maggots is strongly against the view that the parasite 

 gains entrance to the host by the eggs being swallowed, though it is 

 possible that the young maggots are. A few days after eggs have 

 been laid, the skin may be seen to be perforated with minute holes 

 from which flows a watery discharge. On squeezing the skin of the 

 earliest " case " that could be obtained, some clear watery fluid exuded 

 from the holes a smear of which was found to contain a newdy-hatched 

 maggot of H. lineatum. In an experiment at Ballyhaise, seven first- 

 stage maggots were placed on a closely clipped patch on the shoulder 

 of a calf. Immediately they were put on the hairs they crawled down 

 them to the skin, directed their bodies perpendicularly to its surface 

 and soon began to disappear slowly into the skin. Some of them 

 were watched cutting into the epidermis with their mouth-hooks, and 

 it took them about six hours to get beneath the surface. These and 

 other observations confirm the belief that the maggot enters the 

 animal's body through the skin and not through the mouth or gullet. 

 It still remains, however, to be considered how the parasite finds its 

 way to the animal's back, as the eggs are laid on the lower parts. It 

 is also unknown where the larva assumes the second-stage form 

 The sub-mucous coat of the gullet would appear to serve as a norma 

 resting-place for the parasites on their way to the back. The maggots 

 appear to wander to and fro along the gullet during the late autumn 

 and winter, but their general trend is from the pharynx backwards. 

 The most interesting observation in connection with the migration 

 of second-stage maggots is their recognition just outside the muscular 

 coat of the gullet, as if they had bored through from the subcutaneous 

 coat. No maggots were found within the vertebral canal where they 

 have been seen by many Continental observers. Second-stage maggots 

 were, of course, found beneath the skin from January onwards, becom- 

 ing replaced by third and fourth-stage larvae as the season advanced. 



