July i, 1921 
Larval Stages of H. bovis and H. lineatum 
447 
observed that there was a vast difference in these organs of part of the 
eastern specimens, and that the others out of the same lots were identical 
with H. lineatum collected locally. Several thousand specimens of 
fourth- and fifth-stage larvae collected in all parts of the United States 
during the past four or five years were all carefully examined, and the 
fourth-stage larvae that showed stigmal plates differing from H. lineatum 
were recorded. When these records were then compared with those of 
the fifth-stage larvae it was found that all fourth-stage specimens desig¬ 
nated as H. bovis were from localities where H. bovis is present and out 
of lots that usually contained fifth-stage H. bovis larvae. 
Table IV. Distribution of spiny armature on the segments of fourth-stage H. bovis larvce 
based on 29 specimens studied 
Spines on segments 
No. 
Ventral. 
Ventro-lateral. 
Medio-lateral. 
Dorso-lateral. 
Dorsal. 
Ante¬ 
rior. 
Poste¬ 
rior. 
Ante¬ 
rior. 
Poste¬ 
rior. 
Ante¬ 
rior. 
Poste¬ 
rior. 
Ante¬ 
rior. 
Poste¬ 
rior. 
Ante¬ 
rior. 
Poste¬ 
rior. 
2 to 9. 
29 
29 
O 
O 
O 
O 
O 
O 
O 
O 
2 to 8. 
0 
O 
0 
O 
O 
0 
O 
O 
0 
0 
2 to 7. 
O 
O 
0 
O 
O 
0 
O 
O 
O 
O 
2 to 6. 
O 
0 
16 
9 
0 
0 
O 
O 
O 
O 
2 to 5. 
O 
O 
13 
19 
O 
0 
O 
O 
O 
O 
2 to 4. 
O 
O 
O 
I 
12 
°I 
12 
O 
O 
0 
2 to 3., 
0 
O 
O 
O 
17 
4 
17 
5 
8 
0 
2. 
O 
O 
O 
O 
O 
15 
O 
24 
18 
I 
3 . 
O 
O 
0 
O 
O 
I 
O 
0 
O 
0 
Spineless. 
O 
0 
0 
O 
O 
8 
O 
3 
3 
28 
Total larvae. 
29 
29 
29 
29 
29 
29 
29 
29 
29 
29 
a Segment three unarmed. 
The characters of the stigmal plates in the fourth-stage larvae can not 
be seen or the species distinguished with the naked eye as they can be in 
the fifth stage, but with the aid of a low or medium power microscope 
they are distinct. If the specimen is placed 
under the microscope in a vertical position 
with the posterior stigmal plates upward and 
so arranged that they can be viewed at right 
angles to the surface, the structure is visible. 
H. lineatum (fig. 7) presents a group com¬ 
posed of about 20 ring-like or disk-shaped ^ 77 , ^ 
structures constituting the respiratory areas. rior stigmal plates of fourth-stage 
These disks, as they may be designated, ap- larva * Greatly enlar ged. 
pear in a group forming a circle or almost any other shape. The color 
of the disks, which of course is the color of the entire plate, is yellowish 
or yellowish brown. Most of the individual disks are loosely connected 
by their borders or are often separated either singly or in small groups, 
