454 
Journal of Agricultural Research 
Vol. XXI, No. 7 
Koch (7), a veterinarian of Denmark, briefly mentions the fact that 
he observed spines on the very small larvae which he found in the esoph¬ 
agus and states that this is the first-stage larva. He further claims that 
the first-stage larva molts for the 
first time after it has reached the 
back and has punctured the hide. 
His reasons for this statement are 
that— 
LMMM'Jr 
Fig. 2i.—Hypoderma lineatum: Lateral view of first- 
stage larva. Caudal segment halfway telescoped. 
Approximately X 116. 
- ^ 
While the larva is in the early part of 
this stage (first stage) it is clear as glass 
and transparent, but later it becomes 
yellowish white, and while the armature of spines is easily observable in the young 
larva they are less noticeable in the older larva, partly because these are more opaque 
and partly because the dark color of the spines gradually is lost; and finally it may be 
stated as a third reason that the spines are not only comparatively but actually smaller 
in the older larva. It seems as if they become somewhat worn during the migration 
through the body of the cattle, but it is certain that they re¬ 
main present and in the same arrangement on the body of the 
larva throughout this entire period. 
Attention has already been called to the spiny ar¬ 
mature of the second stage or small larva found in 
the esophagus as the principal difference between 
this stage and the larger or third-stage larva found in 
the esophagus and in the back. This alone should 
be sufficient to convince even the most severe critic 
that these are larvae of two distinct stages. How¬ 
ever, it may be stated further that if the spiny arma¬ 
ture became “ worn,” as Koch stated, it would nev¬ 
ertheless leave at least a scar or mark in the skin 
where these spines had been located; but there are 
none to be found, not even under very high magni¬ 
fication, and it seems impossible that the spines could 
have been cast off without also casting off the skin. 
It is true that there is quite a difference in the 
amount and the arrangement of the spiny armature Fig - 22 —Hypoderma imea 
found on different specimens of the smaller larvae 
taken from the esophagus, but this difference is not 
more marked or unusual than that which is encoun¬ 
tered in different specimens of either the fourth or 
fifth stages, and as a whole the change in character 
and arrangement of the armature from the fourth to the fifth stage is not as 
marked as the change found between the second-stage larva in the esoph¬ 
agus and the almost spineless third-stage larva taken from the esopha¬ 
gus or from the back. 
turn: Cephalopharyngeal 
skeleton with spine and 
mouth hooks of first-stage 
larva. A,spine; B, ante¬ 
rior, and D, posterior, end 
of mouth hooks; C, tooth. 
Greatly enlarged. 
