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BULLETIN 1369, U. S. DEPAETMENT OF AGEICULTURE 



has observed the tracks of the larvse up the tendons to the knees or, 

 hocks m the elbow and patellar regions and in some cases farther 

 up the legs; no larvae, however, were recovered in these regions. 



For many years it has been known that larvae of the genus Hypo- 

 derma are found in considerable numbers in the connective tissue 

 between the mucous lining and the muscular coat of the gullets of 

 cattle. Since one of the writers (57) has found a method of deter- 

 mining accurately the species of the larvae in any stage of their 

 development, numerous collections of specimens have been examined 

 from the gullets of cattle in regions where H. hovis occurs plenti- 

 fully, and only one specimen of that species has been found. These 

 observations involved the examination of 1,140 larvae removed from 

 the gullets of 563 cattle, and during every month of the year when 

 they were found to be present in that part of the host. It is safe 

 to conclude from these observations that the larvae of this species 

 do not have the habit of going to the gullet and spending some time 



Fig. 23. — Cow licking heel where larvae of Hypoderma lineatum are penetrating 



there as occurs with H. lineatum. The single larva of H. hovis 

 'found in a gullet was taken at Chester, N. Y., on December 19, 1922. 

 It was 10 millimeters long and was found lying loose on the tissue 

 at about one-fourth the length of the gullet from the pharynx. 



Since it appears that H. bovis does not frequent the gullet it may 

 be taken for granted that all, or practically all, of the published 

 statements of the occurrence of Hypoclerma in the gullet appertain 

 to H. Uneatiiin, and the following discussion relates to that species 

 only: 



The principal data appertaining to the occurrence of the larvae 

 in the gullets are given in Tables 3 and 4. It will be observed that 

 there is a gradual increase in the average size of the larvae from 

 their first appearance to their migration from the gullet. The range 

 in sizes is observed by the writers to be from 1.5 to 16.9 millimeters. 

 Among the larvae found in the gullet only a small percentage are 

 in the third stage, the others being in the second. Hadwen {^O) 

 reports finding in the submucosa of the gullet of a heifer a larva 

 at least 2 millimeters long which he considered in the first stage. 



