HETERODERA RADICICOLA. 403 



of the nervous system by intra-vitam staining with methylene 

 blue and methyl green have not been successful. 



Not even traces of the gonads are to be seen in the larva at 

 this stage. 



The larva may in some cases remain and continue to develop 

 in the original root in which it was produced, but under unfavour- 

 able circumstances, such as result from the decay of the root, 

 it makes its way into the soil. The larva in the soil is able 

 to withstand many adverse physical conditions, such as extremes 

 of moisture, and, to a less extent, of dryness, and of heat. It 

 gradually utilises the food granules stored up in the intestine 

 until that organ at length becomes quite transparent and almost 

 devoid of granules. 



When observed soon after emerging from the egg, the tail of 

 the larva always tapers to an acute extremity. However, larvae 

 isolated from soil, first sterilised by heating and then infected 

 with infested roots, nearly always have an obtusely rounded tail. 

 This indicates the probability of the larva undergoing an ecdysis 

 in the earth. Other evidence of discarded cuticles found in the 

 soil and of larvae with loose fragments of cuticle attached to 

 them confirms this view. 



On reaching a growing plant the larva seeks a, tender portion 

 of the young root, such as the growing point, and making use of 

 the buccal spear, forces an entrance. It eventually makes its 

 way into the vascular tissues of the root and commences to 

 absorb the plant juices and to grow. The largest larvae found 

 in infected roots measured from 500/x to 520/x in length, and 

 23 tx in thickness. 



After attaining this size the larva still continues to absorb 

 food, with the result that the body becomes much broader and 

 decreases correspondingly in length. The spear, oesophagus and 

 other organs in the anterior portion of the body remain un- 

 changed, the thickening being confined to the posterior two-thirds 

 of the body. The larva has now reached the stage represented in 

 Fig. 13. Its length is usually about 400/x, but variations from 

 360/j, to 450/j- not infrequently occur. The width of the body in 

 the region of the oesophageal bulb is approximately 28/x, and the 

 maximum thickness is about 50/x. 



Up to this stage the gonad rudiments are not yet visible. 

 The metamorphosis, which now commences and marks the further 

 development of the parasite accompanying sexual differentiation, 

 is complicated, and is characteristic of the genus Heterodera. Tins 

 metamorphosis, about to be described, has been compared with 

 the development of the Lepidopteran imago inside the chrysalis 

 or cocoon. 



The Development of the Male. 



The larva having already commenced to feed and to set up 

 a large reserve food supply, is by this time more or less perma- 

 nently fixed in position in the root. Feeding gradually ceases 



