12 
BULLETIN 842, U. S. DEPARTMENT OF AGRICULTURE. 
favorable environmental conditions. They develop quickly 
into the so-called second larval stage, presumably by going 
through one or more molts. 
It is in this second stage that the larvae are found as they 
occur in mature flower galls of wheat, a cross section of one 
of which is shown in Plate VI, A. These larvse, Plate V, i?, 
are slender, cylindrical to spindle shaped animals, slightly 
blunt at the anterior end, but tapering to a fine point at 
the posterior end. An outline drawing of a single specimen 
which measured 884 \i in length is shown at a magnification 
of 190 diameters in figure 4. In their greatest width the 
larvse are from 15 to 20 fjt., or about one forty-fifth of the 
average length, which is from 850 to 890 \l. Based on the 
measurement of 184 individuals taken from 16 lots of galls 
collected at as many different localities, the writer found 
an average length of 869 jji, the extremes being 770 p and 
966 \l. These figures are somewhat smaller than those 
suggested by Marcinowski (22), who gives 
the uncertain average larval length of about 
1 mm. Dimensions of larvse from Euro- 
pean as well as American material are 
somewhat larger than those observed by 
the writer with similar material from China. 
The average of all measurements of larvse 
from a single lot of galls from one point in 
China was found to be 793 p, with a maxi- 
mum range in length from 658 to 910 p. 
The dimensions of these larvse from China 
are thus seen to average slightly smaller 
than those examined from other sources. 
This is similar to the condition pointed out 
for the eggs from the same material, namely, 
that they, too, average somewhat smaller. 
The above indicates that possibly there may 
exist morphologically different strains or 
varieties of the organism in different geo- 
r graphical regions. 
As is the case with most nematodes 
parasitic on plants, the structure of the 
Fig. 3. 
Fig. 3. — Youug larva, 500 
-/ 
Fig. 4. 
n in length, which has just emerged from the eggshell. Camera- 
lucida drawing of lateral view. X 190. For an explanation of the letters A to I, see 
figure 4. 
Fig. 4. — Old larva, SS4 ^ in length. Camera-lucida drawing of lateral view. X 190. A, 
nollow probing spear, through which food is sucked ; H, muscular esophageal bulb func- 
tioning as a pump in sucking food through the spear ; C, esophageal canal ; D, posterior 
esophageal bulb ; E, digestive system ; F, nuclei of cells comprising the intestine ; G, 
reproductive system at an early stage ; U, anal opening ; /, tail. 
