is simple, consisting of a body wall containing the alimentary canal 

 (oesophagus, intestine and rectum) and the almost indistinguishable 

 rudiments of the sexual organ. In these respects it is very similar 

 to the free living species. In its anterior end, however, within the 

 mouth opening, is seen a structure not found in the ordinary forms. 

 This is a small spear like organ, (PI. V., s, tig. 5,) which can be moved 

 about to a certain extent and assists the worm in penetrating roots. 

 Most of the young worms when hatched are in the interior of the 

 galls on the roots. They are able to escape without difificulty since 

 the gall becomes decayed and disorganized and since their small size 

 makes it an easy matter to force their way through the tissue, between 

 the cells. Arriving in the soil they at once proceed to attack new 

 roots if any be present, or if not they are able, as our experiments 

 have shown, to exist for a considerable time without change, await- 

 ing an opportunity for further development. Plate VII., fig. i, 

 shows young worms entering the tip of a rootlet. In this they no 

 doubt make use of the spear like arrangement in forcing their way 

 in. Having once effected an opening they are able to force their 

 way between the loose cortex cells without difficulty. Having pene- 

 trated the root so that the whole body is covered, the worm comes to 

 rest and its remarkable course of development proceeds. It does not 

 simply increase in size retaining the same general form, as do the 

 ordinary nematodes, but it begins to increase in diameter in the 

 middle of the body, and in the course of about a week has a sort of 

 spindle shape, broad in the middle and tapering towards both ends, 

 (PI. IV., figs. 3 and 4). From now on the swelling occurs more rap- 

 idly at the tail end, giving the body a club shape, (fig. 5). Thus far 

 the sexes are indistinguishable but now appears a remarkable differ- 

 ence in their mode of development. The female continues to enlarge, 

 but the male undergoes a remarkable transformation and returns- 

 to the slender, worm like form. 



(b) DEVELOPMENT OF THE MALE. 



Up to this point the development of the male, like that of the 

 female, has consisted of an enlargement and broadening of the body. 

 It now, however, ceases to enlarge in this way and begins to draw in 

 from the body wall and increase in length inside the wall, which 

 keeps its original shape, though it is now simply a sac enclosing the 

 worm with which it has no connection. The transformation whick 



