June 15,1921 Life-History Studies of Three Jointworm Parasites 411 
ments with the exception of the ninth, which bears a partial double row 
irregularly placed. Setae are of uneven length as in previous instar 
Full-grown larva (fig. 4).—Color: Larva has a slight ferruginous 
tinge, due to the setae; the body is dirty whitish with a dark central 
area, due to the contents of the digestive tract; the average length of 
5 larvae was 3.108 mm., and the greatest width averaged 1.106 mm. In 
this stage the larva is less pointed, broader, and thicker and much more 
hairy than at any previous stage; setae cover the entire surface of the 
head except for a narrow line down the center of the face; there also 
seems to be a slightly chitinized area down the face on each side of this 
median line. Antennae apparently the same as in previous instars. 
Mouthparts (PI. 76, F): Mandibles (PI. 76, E) same as in previous instar 
with the exception that they are considerably larger. Labrum consists 
of a simple triangular piece and is only very slightly chitinized; maxillae 
and labium exist only as fleshy lobes slightly chitinized on their surface 
Fig. 4. —Ditropinolus aureoviridis: Full-grown larva. X 24.5. 
and bear 8 setae and 4 groups of slight elevations or tubercles. (See PI. 
76 , F.) 
The setae of the body are longer and much more numerous than in the 
previous instar; each segment except the last four abdominal bears an 
irregular row of very long setae around it; in addition, the first thoracic 
segment bears a second irregular row of varying length around it; the 
second thoracic segment bears a second row likewise and a partial third 
around it; the third thoracic segment bears only one additional row 
around it; the first abdominal segment bears a partial second row; the 
second, third, fourth, fifth, and sixth the same. The seventh, eighth, 
and ninth bear numerous setae, varying greatly in length, that can 
scarcely be designated as constituting definite rows; the last segment 
bears numerous small setae and is invaginated laterally. 
In order that the number of larval instars might be ascertained, the 
larvae were kept under almost constant observation under the micro¬ 
scope night and day from the time they were hatched until they became 
full-grown. By this method there appeared to be four fairly distinct 
larval molts, as indicated by the external changes of the larvae. These 
observations were verified by making balsam mounts of the cast skins of 
