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Explanation of Plates. 



Plates I. and II. Development of a free. living nematode, Rhab- 

 ditis sp. PI. I. Figs. 1-12, development of embryo in the egg. X3S0. 

 Fig. 13, young worm just hatched; m, mouth; o, oesophagus; x & b, 

 oesophagal bulbs ; s, stomach or intestine ; r, rectum ; a, anus ; p, 

 location of sexual organ, shown more enlarged in fig. 14. Figs. 15, 

 16, 17, further development of the female, showing ovary at o, and 

 vulva at V, fig. 17. Fig. 18, male and female in copulation. Figs. 

 13, 15. 16, 17, 18, X 135- Plate II. Figs. 1-4, further develop- 

 ment and maturity of female. Fig. 3, mature female; i,lips; o, 

 oesophagus, with x and b bulbs; s, stomach; r, rectum ; a, anus; v, 

 vulva; e, eggs. in various stages; w, young worms. Fig. 4. dead 

 mature female filled with young. Fig. 5, mature male. Fig. 6, 

 posterior end more enlarged ; z, bursa ; q, spicule ; y, anus ; u, 

 spermatozoa. Figs, i, 2, 3, 4, 5, X 135. 



Plate III. Figs. 1-16, eggs of Heterodera radicola, showing 

 development of the embryo. X 325. 



Plate IV. Development of the female Heterodera. Fig. i, young 

 worm just hatched. Figs. 2, 3, and 4, stages of development in the 

 swelling up process of the female. Fig. 5, stage at which copulation 

 takes place; h, spear; k, bulb; g, vulva; e, anus; c, ovary; w, 

 stomach or intestine ; d, rectum. Fig. 6, mature female with ovary 

 tubes partly visible. All X 100. Fig. 7, ovary, more enlarged. 



Plate V. Development of male Heterodera. Fig. i, just hatched, 

 indistinguishable from the female. Fig. 2, beginning of male 

 metamorphosis, showing the body drawing in from the wall, and at t, 

 the rudimentary testis. Fig. 3, same in later stage. Fig. 4. mature 

 male, about to emerge from old body covering. Fig. 5, mature 

 male ; c, cap-like thickening on head ; s, spear ; e, excretory canal ; 

 t, testis; x, spermatozoa; i, intestine. Figs, i, 2, 3, X 175- Fig. 4, 

 X 90. Fig. 5, X 500- 



Plate VI. Sections of normal and nematode-attacked cucumber 

 roots, at various ages. Fig. i, very young, normal root. Fig. 2, 

 mature, normal root ; c, cortex ; p, central cylinder ; d, ducts. Fig. 

 3, young root same age as fig. i, attacked by nematodes. Fig. 4, 

 same, one week later. Fig. 5, section of mature gall, showing dis- 

 tortion of tissues. All X 20. 



Plate VII. Fig. r, tip of cucumber root with young nematodes 

 just entering, enlarged. Figs. 2, 3, and 4, seedlings of rape, cucum- 



