July i, 1921 
Larval Stages of H. bovis and H. lineatum 
453 
v 
ptell 1 
if-:-;- 
mi; I 
Fig. 18.— Hypoderma lineatum: Lateral view of second-stage 
larva. X 13* 
this band broadens out again and envelops the hom-like appendage. 
The base of this appendage is surrounded by a dense group of small 
spines. The posterior border of these segments is covered with small 
spines, decreasing in number 
and size toward the border. 
Aside from the greater size 
of the third-stage larvae after 
reaching the back, the sec¬ 
ond stage may be easily dis¬ 
tinguished by the distribu¬ 
tion of armature. In the third stage the spines on the cephalic segment are 
fewer and are clustered beneath the mouthparts and not scattered as in 
the second instar. In the third stage the armature is absent from all the 
following segments except the 
caudal. The few spines that 
are left below the mouthparts 
of the third stage and the flat¬ 
tened spines on the border of 
the posterior spiracles are ac¬ 
tually smaller 
and more in¬ 
distinct than 
they are in 
the second 
stage, while 
the numerous 
Fig. 19.— Hypoderma linealum: Posterior spiracles and spiny gnineS with 
armatureon caudal segment of second-stage larva. X 100. ^ 
enlarged 
bases surrounding the posterior spiracles of the third 
stage are considerably larger than those in the second 
stage. 
Riley (9), in his description of the second-stage larva, 
states that the larvae in the esophagus measure from 11 
to 14 mm. and are spineless except for a cluster above the 
mouthparts and the posterior half of the caudal segment. 
This description agrees in practically all respects with lineatum/v°en t rTi 
the third-stage larva of both species and is undoubtedlv viewof first-stage lar- 
u . ... - .... J va - A, Mouth hook; 
mat ol a tnird-stage larva taken from the esophagus, b, anterior spiracles; 
It is certain that Riley would not have overlooked the s C k e “to„“«en?i 
spiny armature of the larvae of the earlier stage if any spinesonborderofpos- 
of them had been studied. This may be further sub- posterforTpir’alVi’s.’ 
stantiated by the fact that the writer has obtained as x I21 ' 
many as 20 specimens, ranging from 11.7 to 14.6 mm. in length in one 
lot taken from the esophagus, that were all in the third stage. 
/; a. 
