680 EXPERIMENT STATION RECORD. 



Dehorning cattle, P. V. Ewing {Georgia Htu. Jiiil. Ill {191.'t), pp. 193-201i, 

 I'KJK. 7). — A i)0])iil;ir illustrated accouut. 



The warble flies: Fourth report on experiments and observations as to 

 life history and treatment (Dt'ijt. Ayr. and Tccli. I)usir. Irclund Jour., 15 

 (lyiJf), No. 1, pp. 105-132, pis. 4, fiffS. 2). — This is a report of investigations, 

 conducted in continuation of those previously noted (E. S. Pi., 24, p. 61), which 

 have extended up to the summer of 1914. 



In the first part of the report New Facts in the Life History (pp. 105-119) are 

 presented by G. H. Cari)enter, T. li. Hewitt, and T. K. Reddin. It is pointed out 

 that while Ilypoclerma lineatum lays her eggs on the hairs in i-ows and must, 

 therefore, cling on for a few minutes while depositing them, //, havis lays her 

 eggs singly and quickly, thus causing the animals to get veiy excited. Studies 

 of the external reproductive organs of H. lineatum and II. hovis show that they 

 may be distinguished by very definite structural characters (E. S. R., 31, p. 2.54). 



Up to the summer of 1913 the first-stage larva of the warble fly had not been 

 observed outside the egg, but during that summer it was seen by Glaser in Ger- 

 many (E. S. R., 32, p. GO) and by the authors in Great Britain. The so-called 

 first-stage maggots mentioned by various authoi's as found in the gullets of 

 cattle are in reality early second-stage larvte. 



"The newly-hatched maggot, though only 0.8 mm. (^ in.) long, is dis- 

 tinguished by the relatively immense strength of its mouth hooks, and of the 

 spiny armature in transverse rows across its segments especially on the ventral 

 aspect. . . . The whole aspect of this little larva suggests that it could bore as 

 readily through the skin as through the mucous coat of the gullet. That it does 

 bore into the skin we are convinced as the result of the muzzling experiments 

 and of the direct observations that we have been able to make." 



Muzzling experiments indicate that there is no protection from warbles for 

 those calves which can not lick themselves, and confirm the opinion derived 

 from the early muzzling experiments that the maggot usually enters the host's 

 body through the skin. The experiments indicate that the tongue, far from 

 aiding the parasite in its career, rather inhibits its progress and reduces the 

 number of maggots found in animals that can lick themselves. In an experi- 

 ment conducted during the summer of 1913 three of six calves kept housed and 

 never allowed outside where they would be exposed to warble flies were fe<l 16 

 newly-laid H. hovis eggs each, the other three being kept as controls. All of the 

 calves failed to develop warbles, thus telling strongly against the view that the 

 parasites gain entrance to the host body by the eggs being licked in. 



It is pointed out that the fly deposits its eggs almost exclusively on the legs, 

 not confining itself to any particular part, but showing a decided preference — at 

 least as regards H. boiHs — for the heel or hock joint of the hind limbs. It was 

 observed that a few days after the eggs had been deposited that a soreness 

 appeared in the neighboring region of the skin which was followed by a dis- 

 charge. "On looking with a lens at the skin near the newly-laid eggs, we saw 

 that it was perforated with minute holes from which flowed a watery discharge, 

 hardening on the surface to form a scaly deposit. After a day or two the region 

 became covered with small pimples which disappeared a few days later. On 

 squeezing the skin of the earliest ' case ' that could be obtained, some clear 

 watei*y fluid exuded from the holes, and on examining a smear of this under the 

 microscope we were delighted to find a newly-hatched maggot of H. lineatu))i." 



In an experimental attempt to verify these observations the authoi's clipped 

 closely a small patch on the shoulder of a calf and placed seven maggots 

 thereon. " Immediately they were put on the hairs they crawled down 

 them to the skin and directed their bodies perpendicular to its surface. We soon 



