June is, 1921 
Life-History Studies of Three Jointworm Parasites 417 
LARVA 
First instar (fig. 10).—Newly hatched larvae are translucent whitish 
in color; the average length of three larvae in this stage was 0.3945 mm. 
and the greatest width, 0.1490 mm. When hatched the larva tapers 
toward each extremity but is pointed posteriorly; it is very smooth, the 
setae being so small that it is practically impossible to determine the 
exact number. There is a pair of prominent fleshy elevations or tubercles 
on the front of the head that are apparently the antennae. The head is 
very smooth, and if any setae are present they are so small that it is 
almost impossible to ascertain their number and position. The man¬ 
dibles (PI. 76, G) of the first instar are simple hooks, very slightly chiti- 
nized, very pointed at tips, and broad at the base. The body consists 
of the usual 13 segments and bears 5 pairs of spiracles, a pair to each of 
the last 2 thoracic and first 3 abdominal segments. The external changes 
in the succeeding instars were so slight that it was impossible to identify 
them accurately. A balsam mount was made of the entire contents of 
one of the glass cells where an individual larva had developed and 5 
pairs of mandibles (PI. 76, G-K) 
were found. As all of these pairs 
gradually increased in size it is rea¬ 
sonable to suppose that they were 
those of Homoporus chalcidipliagus . 
One pair (the fourth) differs slightly 
in shape from the other four pairs, 
though in size it fits in as the fourth pair. The slightly different shape of 
the fourth pair of mahdibles is probably due to the fact that the 
mandibles are difficult to mount so as to have all the pairs in the same 
relative position, and probably the fourth pair was viewed from a 
slightly different ailgle when it was illustrated. No illustrations other 
than those of the mandibles were made of any of the larval instars, 
except the first and the full-grown larvae, since none of the other instars 
could be determined accurately. 
Full-grown larva (PI. 74, D; fig. 11).—Color dirty whitish, with a 
dark line showing through the center of the larva due to the contents of 
the digestive tract. The average length of five full-grown larvae was 
3.08 mm., and the greatest width was 0.91 mm. The full-grown larva is 
of the same general shape as the first-instar larva. The last abdominal 
segment is clearly invaginated laterally. The head (PI. 76, M) is very 
smooth and bears a pair of rather prominent fleshy elevations or tubercles 
on the front that are evidently the antennae. It also bears four pairs of 
very small setae one pair laterad of the mandibles; a pair laterad of these, 
about the middle of the cheek; a pair dorsad of these; and a fourth pair 
above and inside the antennal region. There are three pairs of minute 
Fig. 10 .*—Homoporus chalcidiphagus: Lateral view of 
first-instar larva. X 128. 
