ever, by examining galls from affected plants at frequent intervals 

 during their formation, it becomes evident that at the time when the 

 females are mature the males have ceased to exist, but that they 

 may be found without difficulty if looked for at the proper time. 



C. DEVELOPMENT OF THE FEMALE. 



The early stages of the female worm are similar to and indistin- 

 guishable from those of the male. It does not, however, return to the 

 worm-like form after once entering the root and beginning to swell 

 up, but continues in the same way until it comes to have the gourd- 

 like shape shown in plate IV., fig. 6. This swelling affects the body 

 wall and also the intestine, which enlarges correspondingly. The 

 animal retains its pointed tail-like process up to the stage when the 

 male can be distinguished, but soon after this disappears and the 

 posterior end of the body assumes a roundish form. This change 

 takes place by the " moulting " or casting of the skin, a process 

 which takes place several times (four or five) during the development 

 of the worm. This moulting is very similar to that of insect larvae, 

 the skin lining the oesophagus being cast as well as that of the 

 exterior of the body. Plate IV., fig. 4, shows the female at the time 

 when the male is just becoming distinguishable (plate V., fig. 2,) and in 

 plate IV., fig. 5, the female is represented about one week later, i. e. at 

 the time when the male has completed its transformation and become 

 mature. At this stage the intestine of the female has become very 

 broad at the posterior end and contracts suddenly to a narrow por- 

 tion or rectum leading to the anus. The ovary has been developing 

 from the immature sexual organ and now consists of a two-branched 

 tube, starting at the posterior end of the body, where the sexual 

 opening is just appearing close by the anus. The simultaneous 

 maturing of the male and development of the sexual opening of the 

 female leave but little doubt that copulation now takes place, though 

 we have not actually observed it as we did in the free living form. 

 The return of the male to the worm-like form is evidently an adapta- 

 tion to enable it to reach the female, which is entirely immov- 

 able after entering the root. It is not probable, however, that 

 the male is obliged to travel a great distance in order to find its 

 mate, as the worms show a sort of gregariousness in entering the 

 root and usually several locate near one another. The European 



