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Vol. XXI, No. 7 
medium power of the microscope, are very reliable and serve to differ¬ 
entiate the species readily. The forked anterior end and the blunt rear 
end of the mouth hook of H. bovis are so distinctly different from the 
sharply pointed anterior end with a well-formed tooth some distance 
below and the slightly pointed rear end of the hook of H. lineatum that 
the two species can be separated almost at sight in the first instar. 
The mouth hooks of the first, second, and third stages do not change in 
structure with specimens of the same species except that they become 
slightly heavier, somewhat shorter, and stouter in the second and third 
Fig. 24. Hypoclerma bovis: First-stage larva. I, Lateral view; II, ventral view; III, cephalopharyngeal 
skeleton with spine and mouth hooks; IV, caudal segment. Ph, Skeleton of pharynx; H, mouth hooks; 
M, spine; Tr, air tubes; P sp., posterior spiracles. (Carpenter and Hewitt.) 
stage, but the two almost parallel rods or arms of the cephalopharyngeal 
skeleton of the first-stage larva spread considerably posteriorly and be¬ 
come heavier in the second and especially in the third stage. 
LITERATURE CITED 
(1) Brauer, Friedrich. 
1863. monographie der oESTRiDEN ... 291 p., 10 pi. Wien. Literatur, 
p. 6—l8. 
(2) Carpenter, George H., Hewitt, Thomas R., and Reddin, T. Kerry. 
1914. THE WARBLE-FLIES. FOURTH REPORT ... I. NEW FACTS IN THE LIFE- 
HISTORY. In Dept. Agr. and Tech. Instr. Ireland Jour., v. 15, 
n °. 1, p. 105—119, [4] pi. 
