450 
Journal of Agricultural Research 
Vol. XXI, No. 7 
position with the anterior end upward and so arranged that the anterior 
spiracles appear in the center of the field and the mouthparts near the 
edge, one can see a single, small, but distinct, hom-like appendage at a 
distance about equal to that of the mouthparts and in a direction from 
the spiracles opposite from the mouthparts. There are no spines around 
the base of this appendage, which is smaller and more indistinct in this 
Fig. ii .—Hypoderma bovis: Cephalo- 
pharyngeal skeleton and mouth hooks 
of third-stage larva. A, spine; B, 
anterior end, and C, posterior end, 
of mouth hooks. X 125. 
Fig. 12 .—Hypoderma bovis: Posterior spira¬ 
cles and spiny armature on posterior half 
of caudal segment of third-stage larva. 
Greatly enlarged. 
larval stage than in the two younger stages and is entirely absent or 
invisible in the two larger stages. 
DESCRIPTION OF THE SECOND INSTAR OF H. UNEATUM 
The second-stage larva has not been recognized heretofore as an instar 
distinct from that later found in the esophagus and in the back, hence it 
will be rather fully described. The smaller larvae found in the gullet are 
in this stage. Specimens ranging from slightly less than 3 mm. in 
length and upward have been collected from esophagi of slaughtered 
cattle at Fort Worth (Tex.) packing houses as early as April 1. During 
May, 1920, a considerable number of larvae, all of this stage, measuring 
from 3 to 6 mm., were taken by E. E. Wehr from esophagi of locally 
raised cattle slaughtered at a Dallas packing house. These examinations 
were continued by the writer at weekly intervals. All the larvae (nearly 
400) examined up to August 15, 1920, were found to be still in the second 
stage. These ranged up to 9 mm. in length. In the general collection 
made by the writer many other specimens ranging up to as high as 14 mm. 
in length also prove to be of this stage. All larvae in this second instar 
