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, Z?, 

 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 [l in length is shown at a magnification 

 of 190 diameters in figure 4. In their greatest width the 

 larva? are from 15 to 20 p., or about one forty-fifth of the 

 average length, which is from 850 to 890 y.. 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 \x, the extremes being 770 \i and 

 966 [x. 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 [*, with a maxi- 

 mum range in length from 658 to 910 \l. 

 The dimensions of these larva? 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- 

 graphical regions. 



As is the case with most nematodes 

 ./ parasitic on plants, the structure of the 



Fig. 3. 



Fig. 3. — Young larva, 500 11 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, 

 Hollow probing spear, through which food is sucked ; B, 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 ; O f 

 reproductive system at an early stage ; II, anal opening ; I, tail. 



Fig. 



