446 
Journal of Agricultural Research 
Vol. XXI, No. 7 
plate of H. bovis remain constant throughout the fifth larval instar and 
also are distinct in the puparia. 
DIFFERENTIATION OF THE FOURTH INSTAR OF H. BOVIS AND H. 
LINEATUM 
Available literature on the two species of Hypoderma under consid¬ 
eration gives no description of distinct characters for the identification 
of the fourth (heretofore known as the third) larval stage. Tabulations 
of the spiny armature of many fourth-stage larvae of H. lineatum (Table 
III) and of H. bovis (Table IV) revealed that there was no constant 
character of the armature in either species. The ventral posterior 
border of segment io, which is always covered with spines in the fifth 
larval stage of H . lineatum and always naked in H. bovis , is nearly 
always naked in the fourth instar of both species. The armature on the 
dorsal surface and on the lateral divisions, as given in Tables III and 
IV, shows that it varies with different specimens of either species as 
greatly here as it does in the fifth larval stage. 
Table III .—Distribution of spiny armature on the segments of fourth-stage H. lineatum 
larvae based on 114 specimens studied 
Armature on seg¬ 
ments 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 10.. . . 
I 
3 
O 
O 
O 
O 
O 
O 
O 
0 
2 to 9. 
94 
no 
0 
0 
0 
O 
O 
O 
O 
0 
2 to 8. 
19 
I 
O 
I 
O 
O 
O 
Oi 
O 
O 
2 to 7. 
0 
0 
b 3 
I 
O 
O 
O 
0 
O 
O 
2 to 6. 
0 
0 
c 3 7 
7 
O 
0 
O 
0 
O 
O 
2 to 5. 
0 
0 
41 
52 
O 
0 
2 
0 
O 
O 
2 to 4. 
0 
0 
28 
8 
39 
O 
55 
1 
0 
O 
2 to 3.. . . . . 
0 
0 
5 
2 
72 
O 
54 
18 
2 
O 
3 to 4. 
0 
0 
0 
3 
0 
I 
0 
1 
O 
O 
3 to s. 
0 
0 
0 
22 
0 
I 
0 
0 
0 
O 
4 to 5. 
0 
0 
0 
5 
0 
I 
0 
0 
0 
O 
6 to 7. 
0 
0 
0 
0 
O 
O 
0 
0 
0 
I 
2. 
0 
0 
0 
1 
. 3 
3 
3 
35 
69 
O 
3 . 
0 
0 
0 
4 
0 
5 
0 
0 
0 
O 
4 . 
0 
0 
0 
4 
0 
1 
0 
0 
0 
I 
5 . .••• 
0 
0 
0 
2 
0 
0 
0 
0 
0 
O 
Spineless. 
0 
0 
0 
0 
0 
102 
0 
58 
43 
112 
Total larvae.. . 
114 
114 
114 
114 
H 4 
114 
114 
114 
114 
114 
a Segments 4 to 6 unarmed. 
b One specimen with segment five unarmed. 
c Three specimens with segment five unarmed. 
In studying the characters of the stigma! plate of fourth-stage larvse 
collected at Dallas, Tex., and elsewhere in the southern States where 
only H, lineatum exists, and comparing them with specimens collected 
in the northeastern States where both species are found, it was soon 
