July x, 1921 
Larval Stages of H. bovis and H. lineatum 
45i 
were taken from the esophagi and were collected in various localities, 
mostly in the southern States. An effort was made to obtain this stage 
of both species, but so far the writer’s collections of small larvae in regions 
where H. bovis is found apparently were made too early, and only speci¬ 
mens of H. lineatum were obtained. Although a similar stage of H. 
bovis has not been observed so far, it seems reasonably safe to assume that 
it is also present, since the general characters of the four known larval 
stages agree in all respects with those of the first, third, fourth, and fifth 
stages of H. lineatum . The comparisons of the larvae of each stage for the 
two species under considera¬ 
tion have been based on the 
assumption that there are 
five stages of H . bovis . 
The distinguishing char- 
acter of this stage lies in the FlC - n.-HyPoderma lineatum: Lateral view of third-stage 
0 # larva. X 4. 
armature which is present 
on every segment of the entire larva (fig. 17-19). In form, this stage 
is very similar to the third-stage larva at the time it reaches the 
back, but of course it is much smaller and not so distinctly segmented. 
When the armature alone is considered one is led to believe at first sight 
that it is the first-stage larva which hatches from the egg. After closer 
examination and comparison with the armature of the first stage, how¬ 
ever, it can easily be observed that this is an entirely different coat of 
armature. The spines not only differ by being smaller in size but also, 
on the terminal segment at least, differ vastly in structure. While the arma¬ 
ture on the middle segments is not as plain as in the first, fourth, and fifth 
stages, it is nevertheless easily seen with a low power of the microscope 
and appears in transverse 
rows very regularly placed 
on at least the anterior part 
of each segment. On the 
Fig. 14. —Iiypoderma lineatum: Ventral view of third-stage second to fourth Segments 
larva. X 4. . , . ° ' 
inclusive, the spines m the 
anterior row are rather densely placed and are the largest in size. Fol¬ 
lowing the first row are several more irregularly placed rows, in which 
the spines decrease in size and abundance toward the posterior border 
of the segment. On the fifth, sixth, and seventh segments the anterior 
row is also quite regular, but the spines are smaller and farther apart than 
in the same rows of the preceding segments. The spines behind the an¬ 
terior row on these middle segments also decrease in number and size 
in the same proportion as on the anterior segments. On the eighth and 
ninth segments there is a further decrease in size and number of 
spines, and the posterior half of the segments is almost naked, except 
laterally, where small spines extend farther back. The anterior part 
of the tenth segment is covered ventrally with a band of spines 
48495°—21 - 3 
