404 IIETERODERA RADICICOLA. 



and a new cuticle is formed close under the old one. The separa- 

 tion of the cuticle soon begins, and finally the organism becomes 

 an amorphous mass of protoplasmic granules enclosed in the 

 original skin, with its pointed spine-like tail. The spear of the 

 original larva is not retained and eventually disappears, a new 

 spear being produced later. A period of apparent inactivity 

 now ensues, the duration of which may be extended and is not 

 easy to estimate. At any rate, it seems probable that, should con- 

 ditions make it necessary, the further development of the animal 

 can be suspended for a considerable period. 



Indications of the differentiation of the sex of the parasite 

 are occasionally manifested at this stage by the appearance of 

 a mass of dense cells in the posterior part of the body. These 

 cells may be interpreted as the incipient gonads, but as their fate 

 cannot be followed in the later development, their significance 

 cannot be emphasised. At this stage a period of cellular re- 

 arrangement occurs, and after a time the internal mass assumes 

 a vermiform shape. Lengthening then commences, with the 

 result that the worm becomes folded up inside its sac-like larval 

 skin until there are as many as four complete coils. Movement on 

 the part of the worm inside the old skin becomes evident some 

 time before the metamorphosis is complete. Two or three days 

 before the male worm emerges the movement increases in vigour. 

 By this time all the organs of the mature worm are already formed 

 and the spear is seen to be making rapid motions inside the buccal 

 cavity in order to effect an exit. A way of escape is finally found 

 by the rupture of the enveloping sac as a result of the pressure 

 exerted by the worm inside. (Plate VIIT, Fig. 18.) 



This is the second ecdysis that has been observed so far 

 in the evolution of the male. No evidence of further moults by 

 the male worm whilst still enclosed in its old cuticle, such as have 

 been stated by Stone and Smith (1898) to occur, has been obtained. 



On escaping from the larval skin the length of the adult 

 male worm may vary from 590ja to 1,200/a, with an average thick- 

 ness of about 30/t. Further growth is rapid, the worm already 

 commencing to make use of the plant juices in the root. The 

 maximum size of an adult worm that I have met with during 

 these investigations was attained by an individual isolated for 

 nearly three weeks in watch glass with potato cuttings. The size 

 of this individual was approximately twice that of an ordinary 

 large individual, the length being 2,590jh, and the greatest thick- 

 ness 55/a. The sluggish movements of the worm seems to make 

 it improbable that it could come out of the root and travel any 

 appreciable distance through the soil in search of another root, 

 and up to the present time I have not found a single mature 

 male worm of the genus 11 ' eterodera in the numerous water cul- 

 tures of heavily infested soils that I have examined. Nevertheless 

 the male worm possesses considerable powers of resistance towards 

 desiccation and excessive moisture. Yet it does not seem possible 

 that the female parasite could be fertilised by a male other than 

 one which has developed in the same infected root. 



