July i, 1921 
Larval Stages of H. bovis and H. lineatum 
455 
DISTINGUISHING CHARACTERS IN FIRST-INSTAR LARVAE OF H. BOVIS 
AND H. LINEATUM 
Riley (9) described the first-stage larva of H. lineatum (fig. 20-23) 
which he obtained from the egg just before hatching and which does not 
differ in any way from the larva normally hatched from the egg. Careful 
examinations of some of the hundreds of larvae of this species hatched 
from eggs in an electric incubator at the Dallas laboratory agree well 
with Riley’s description; Riley, however, does not mention the anterior 
horn-like appendage, which is large and very distinct in this stage. 
The armature on all the segments except the posterior part of the first 
stage is very dense and considerably larger than on the second stage. 
On the caudal segment of the first stage the spines with an enlarged cir¬ 
cular base are not present, although this segment is well covered with 
spines similar to but larger than those on the preceding body segments. 
The flattened spines (fig. 20; 
23, Fs) on the border of the 
posterior spiracles are more 
than twice as large as the sur¬ 
rounding spines. The dense 
large spines on the body seg¬ 
ments and large flattened 
spines on the margins of the 
posterior spiracles of the first- 
stage larva are in striking con¬ 
trast with the smaller and 
. Fig. 23.— Ilypodcrma lineatum: Posterior spiracles and spiny 
much thinner armature on armature on caudal segment of first-stage larva. P sp., pos- 
the body segments and small terior spiracles; Fs., flattened spines on border of spiracles. 
flattened spines on the border X 5 °° 
of the posterior spiracles surrounded by larger spines with the heavy 
blackish base in the second stage. 
The first-stage larva of H. bovis (fig. 24) was first described by Car¬ 
penter, Hewitt, and Reddin (2). The spiny armature on the cephalic 
and all the body segments is very similar to that of H. lineatum , but the 
arrangement of the spines on the caudal segment differs somewhat, and 
the spines are considerably larger in H. bovis . The flattened spines, 
usually three in number, on the border of the anal spiracles of H. bovis 
appear smaller in comparison with the large surrounding spines and are 
actually smaller than in H. lineatum. The peculiar type of spines with 
large circular bases as found in the second and third stages of H. lineatum 
and third stage of H. bovis is here absent as it is in H. lineatum of the 
same stage. While the armature of the first-stage larva of the two spe¬ 
cies in question may differ somewhat, it is hardly reliable for the differ¬ 
entiating of the two species. The characters of the mouth hooks, however, 
which are here plainly visible in the uncleared specimens with the aid of a 
