HETERODERA RADICICOLA. 407 



until the individual has assumed the shape of a club (Fig. 16). 

 The anus and vulva become situated on a prominent protuberance 

 at the extremity of the body. The anus, which opens to the 

 exterior at the terminus of the short, narrow rectum, is quite 

 terminal, while the vulva which is continuous with the vagina, 

 though in close proximity to the anus, is slightly lateral in 

 position. Both anus and vulva have tumid lips, and it can only 

 be at this stage of the life history that fertilisation by the male 

 is possible, for in later development the vulva disappears from 

 view and the protuberance on which it was situated is absorbed 

 into the general contour of the body. 



The spear, which is 20/i in length, is in constant motion, 

 and since the swollen shape of the body makes progression im- 

 possible the function of this structure can only be that of rupturing 

 the walls of the neighbouring cells and absorbing the liquid 

 contents. The young female (Fig. 16) at the time of fertilisation 

 measures 460/t to 600/x in total length, the maximum thickness 

 being approximately 230/a. 



Structure of the Adult Gravid Female. 



After the fertilisation of the young female, another period, 

 again characterised by an increase in thickness, commences until 

 finally the body attains the pyriform shape of the gravid indi- 

 vidual as illustrated in Fig. 17. This thickening is now primarily 

 due to the formation of eggs inside the uteri. The size of these 

 swollen females ranges from 660/i, to 750/x in length (average 

 700/x), while the maximum breadth varies from 400/x to 495/x. 

 The "neck" region is relatively shorter than that of the female 

 before fertilisation. In the parasite in the potato, which formed 

 the main material for the present investigations, no traces of 

 transverse striations were visible on the anterior "neck" region 

 of the females, even when observed under the highest magnifica- 

 tion, although these were always evident in the parasites of 

 other roots, such as the snapdragon, Antirrhinum majus. 

 Striations were also frequently visible in other parasites taken 

 from infested potatoes grown in other localities. This point will 

 be again referred to in the discussion of the identity of the 

 parasite. 



The spear is about 25/x in length and can be easily seen 

 when moving. The oesophagus is sinuous and its bulb is relatively 

 large, its diameter occupying a large part of the width of the 

 neck." Further details of the anatomy are obscured as a 

 result of the body becoming overladen with food. The excretory 

 duct and its pore have been recognised only in one or two 

 instances. Its position is normal. 



The uteri have undergone considerable tcrsion, and their 

 coils are usually undistinguishable owing to the body of the 

 organism being tendered opaque by its protoplasmic contents. 

 The vulva has disappeared from view, and the anus can only be 

 occasionally distinguished, surrounded by a less opaque area at 

 the posterior spherical region of the body. 



