NEMATODE DISEASE OF WHEAT. 13 



larvse of the wheat nematode is comparatively simple. In general, 

 earch larva consists of an outer tube or body covering, within 

 which is a second smaller tube, the digestive tract. The space 

 between the walls of these two tubes is known as the body cavity. 

 Anteriorly, the digestive system opens at the end of the animal, 

 while posteriorly it opens at the anus, or vent, about 50 ]x from 

 the point of the tail (fig. 4). A buccal spear (9 to 11 pL long) 

 pointed at the forward end and trilobed at the other, is located at 

 the anterior end of the digestive system (fig. 4, A ) . By means of this 

 hollow spear, which can be exserted and retracted by strong muscles, 

 the larva is able to pierce its egg membranes, to force its way into 

 plant tissues, and by means of the fine canal which extends through 

 the spear to absorb plant juices or other liquid foods. Connected to 

 the base of the spear is the rather slender esophagus, which is about 

 one-quarter the entire body length. About midway of the esoph- 

 agus is an almost spherical muscular-walled enlargement known 

 as the esophageal bulb (fig. 4, B). Near the center of this is a small 

 valve capable of expansion and contraction by the muscular wall 

 of the bulb. By means of a pumplike action of the bulb, liquids 

 are sucked through the spear and esophagus and forced into the 

 intestine. Just back of the esophageal bulb, the esophagus is slender 

 and practically cylindrical, but toward its posterior end it enlarges 

 gradually into another bulb known as the posterior esophageal bulb 

 (fig. 4, D). A large light-refractive cell, which functions as a 

 salivary gland, is located near the base of this swelling. This pos- 

 terior esophageal bulb joins with the much larger tubular intestine, 

 which almost completely fills the posterior three- fourths of the tube 

 of the body wall (fig. 4, E). The diameter of the intestine corre- 

 sponds directly with that of the larva except at its posterior end, 

 where the intestine is contracted into a fine channel, the rectum, 

 which terminates at the anal opening. The intestine contains trans- 

 lucent, granular matter, presumably reserve food, in the form of 

 fatty globules and other materials. The body cavity of the animal 

 not occupied by the digestive system is for the most part practi- 

 cally transparent. Usually a row of refractive nuclei of cells com- 

 posing the intestinal wall can be plainly seen, and this, together 

 with the half -moon shaped light zone located about midway between 

 the ends of the intestine, distinguishes the larva of this nematode 

 from those of any other species occurring on wheat. No known 

 sexual differentiation occurs in larvae of the stage just described, 

 although the primordial reproductive organs, consisting of a few 

 hyaline cells located in the half-moon shaped light zone, already 

 mentioned, are always visible. Within the galls, as they mature 

 and dry out, the larvee, all of which appear to have reached about 



