402 HETERODERA RADICICOLA. 



breadth is 15/n. No evidence was seen of the larva having under- 

 gone an ecdysis before emerging from the egg, although special 

 attention was paid to this point. 



The movement of the larva of Heterodera is slow and languid, 

 a feature to be contrasted with the rapid motions made by other 

 free-living and saprophytic nematodes such as certain Tylenchidae. 

 The movement of the larva, even when kept in water, is scarcely 

 such as to indicate any appreciable progress in a definite direction. 

 The structure of the larva (Fig. 12) is that of a typical 

 specimen of the genus Tylenchus, and it is only a consideration 

 of size and mode of movement that might allow one to differen- 

 tiate it from larvae of Tylenchidae. 



The cuticle is relatively thin and transparent, and even 

 under the highest magnification, indications of delicate transverse 

 striae are only occasionally visible. Dermal muscle fields could 

 not be detected under the cuticle, as described by Bessey. 



The anterior end of the larva is conical in shape, and the 

 body, which is almost uniform in thickness throughout the greater 

 part of its length, gradually tapers to a subacute tail. 



The lip region at the anterior end is marked by a small pro- 

 tuberance which is constricted from the rest of t lie body by a 

 shallow groove, and is pierced by the spear. 



The spear is a slender-pointed organ, piobably of a chitinous 

 nature. In the larva it measures from 14/m to 16/a in length. Its 

 breadth is approximately 1.5/x, and it tapers to a point. At its 

 base are three small swellings, symmetrically disposed, to which 

 the oesophagus is directly attached. The spear can be protruded 

 for some short distance through the buccal aperture, and is used 

 as a battering organ when the larva enters the root. It is prob- 

 ably pierced by a very fine canal through which liquid food may 

 be absorbed into the oesophagus. 



The oesophagus is a narrow, slightly coiled, tube, 40/x to 45/j, 

 in length. The lumen is lined with cuticle, and is continuous 

 with the spear. At the posterior end of the oesophagus the lumen 

 is dilated to form a spherical bulb with thick walls, and functions 

 as a suction organ. 



The intestine is the widened pait of the alimentary tract 

 behind the oesophageal bulb. It occupies practically the entire 

 body cavity, and is filled with food globules and irregular granules 

 of varying sizes. The intestine terminates in a very short rectum 

 opening to the exterior by an anus on the ventral surface of the 

 body about 50/x from its extremity. 



The excretory and nervous systems aie difficult to see. The 

 excretory canal can occasionally be observed with an oil-immersion 

 objective as a delicate sinuous duct running in the middle of the 

 body and opening by a pore just posterior to the oesophageal 

 bulb. 



The nervous system is even more difficult to detect. Indica- 

 tions of a few nerve fibres encircling the oesophagus behind the 

 bulb have been observed. Attempts to bring out further details 



