ECONOMIC IMPORTANCE OE NEMATODES. 331 



observations, no ecdysis of the larval cuticle has been noted 

 beiore or soon after the larva hatches from the egg. The 

 laiA'ae pierce their way through the uterine and body walls 

 of the mother, and so escape into the root tissues. They do 

 not appear to grow to any considerable extent after hatching. 

 Morphologicall}-, the larvae cioselj^ resemble those of the 

 genus TyiencUus and Aplielenckxis, and indeed they cannot 

 be distinguished from these except perhaps on a basis of size, 

 the larvae of H. radicicola measuring from 340 to 370 /x in 

 length, with an average uniform breadth of 15 /x. One of 

 the most prominent structures of their anatomy is a chitinous 

 boring organ, the so-called spear, situated in the pharynx. 

 By means of this structure the larva is enabled to pierce a 

 passage out of the root into the soil, where it may lie dormant 

 for a time, then seek out and peuetrate another rootlet. 

 But, should conditions within a root be favourable, the lai'ra 

 may not abandon the root in which it was hatched, but may 

 migrate to adjacent healthv tissues and there undergo sexual 

 differentiation. At any rate, sexual differentiation does not 

 take place outside the tissues of a root. The future sex of 

 the larva cannot be ascertained prior to tlie commencement of 

 the developmental metanioi'phosis. Evidence has recently 

 been acquired by the author which indicates that the larva 

 in the soil undergoes an ecdysis. However, the old skin is 

 not cast, but adheres to the new larval cuticle, giving it a 

 double appearance. Sexual dift'erentiation, which is accom- 

 panied by a profound change in shape and alteration of 

 internal organs, commences soon after the lam-a has reached 

 the vascular tissues of the root and has commenced to absorb 

 nourishment. Both sexes of the parasite swell to a consider- 

 able extent, so altering their primitive Avonu-like shape. 

 Rudiments of reproductive organs appear at a comparatively 

 early stage. 



Within the swollen female larva a new organisation is 

 gradually built up by a process comparable with the formation 

 of the imago insect within the pupa. The new organism, 

 however, does not leave the lai'\'al encasement, but comes to 

 occupy its entire body, assuming the role of the mature female 

 with a prominent external genital aperture. This complicated 

 process must be regarded as another ecdysis, but again the 

 old cuticle is not discarded. Fertilisation of the female can 

 only take place in the root tissues, because the shape of the 

 female will not permit any movement on its part. 



In the development of the adult male, the metamorphosis 

 is even more intense than in the female. The larva, having 

 fed and grown to a certain extent, enters into a state of 

 complete quiescence and seems to be lifeless. But soon the 

 presence of a new individual within the swollen dormant larva 

 becomes manifest. This individual grows and lengthens and 

 assumes a vermiform appearance, coiled up witliin the old 

 body. Finally, this worm escapes from its larval envelope 

 as the mature male, whose length' varies from 700 /x to 2,590 //. 



