48 



Cobb — Nematodes, mostly Australian and Fijian. 



weaker tube, which passes through the oblique nerve-ring, situated just behind the 

 median bulb. The posterior bulb may become rudimentary, but probably never quite 

 disappears. Lateral organs as well as visual organs are unknown in the genus. The 

 female sexual apparatus is usually single and asymmetrical, being in that case usually 

 straight and directed forward though often presenting a rudimentary posterior branch, 

 but it may be double and symmetrical. In the former case the vulva is behind the 

 middle ; in the latter case it is central. The male possesses two equal slightly arcuate 

 spicula and in most species a more or less well developed bursa. 



1. T. radicicola, Greef 



3-2 15- 17-6 Y 87-9 -^ ^^^ formula for the freshly hatched 



Cuticle traversed 



Fig. 4. — Larva of TyUnchua 

 radicicola. 



I, the larva magnified 190 

 times. II, head of the same 

 worm magnified 875 times. 

 Ill, small section of the body 

 magnified 750 times. IV shows 

 at the centre of the circle 

 the actual size of the worm, s, 

 spear ; 6, median sucking-bulb ; 

 n, nerve-ring ; p, ventral excre- 

 tory pore ; posterior 6, cardiac 

 bulb ; i, the intestine ; c, the 

 cuticle ; I, the lateral wings of 

 the cuticle. 



33 3-4 3-6 2-3 



larva, of which the following is a further description 

 by about five hundred transverse striae ; neck cylindroid to opposite the 

 base of the buccal cavity, but thence to the mouth is convex-conoid ; 

 faint indications of lips; three-bulbed spear 

 when at rest drawn back so that its apex is 

 removed half the spear-length from the mouth; 

 ellipsoidal sucking-bulb just in front of the 

 nerve-ring; posterior oesophageal swelling weak 

 and devoid of chitin ; intestine pellucid, two- 

 thirds as wide as the body, and having its cells 

 closely packed with granules ; ventral excretory 

 pore just opposite the commencement of the 



intestine ; lateral wings occupying an area one-fourth as wide as the 

 body and presenting four parallel lines ; tail conical from the incon- 

 spicuous anus ; caudal glands absent, terminus pointed. 



The larvse, which are found in large numbers in the cavities occupied by the 

 parasitic mother-worms, and also in the sur- 

 rounding soil, make their way into the rootlets 

 of various plants by means of the special 

 piercing and sucking apparatus, namely, the 

 spear and bulb, and then undergo a remark- 

 able metamorphosis. At an early moult they 

 lose the conical tail and the posterior end 

 becomes rounded. Meanwhile the body, amply 

 nourished by plant-juices, becomes plump, and 

 takes on the dimensions shown in the fol- 

 lowing formula and the adjacent illustrations : 

 The larva makes its way into a 



17-9 Y 91- 

 3-8 ? 9-5 16-1 6- 



Fig. 5.— Young of Ty- 

 lenchus radicicola, 

 after entering a 

 root. 



«, spear ; h, sucking- 

 bulb ; p, ventral excre- 

 tory pore ; i, intestine ; 

 V, unicellular ventral 

 gland ; u,, anas. 



Fig. 6. — Immature Ty- 

 lenchus radicicola 

 shedding its skin. 



c, the old skin being 

 cast off; s, the old and 

 the new spear ; p, the 

 ventral excretory pore ; 

 V, the unicellular ven- 

 tral gland ; o, rudimen- 

 tary sexual organs. 



rootlet by applying its mouth to the surface of the rootlet and exerting a powerful 



