408 HETERODERA RADICICOLA. 



Gravid females taken from potatoes have been found to con- 

 tain not more than sixty to seventy eggs in all stages of segmen- 

 tation. Not infrequently a number of free larvae are to be found 

 in the body cavity of the now deceased parent. Presumably the 

 majority of the eggs develop and hatch in the uteri and the 

 larvae migrate into the general body cavity whence they escape 

 on the disintegration of the parental body. In the writer's opinion 

 the female cannot be described as oviparous, since evidence of 

 her depositing eggs is lacking. (Of. Bessey, 1911.) 



Identity of the Parasite. 



Qenvs.— Heterodera (A. Schmidt, 1871) is defined by 

 Eailliet in his "Traite de Zoologie medicale et agricole," page 

 554, as a plant parasite nematode, the oesophagus having two 

 bulbs, the anterior cylindrical, posterior spherical. No teeth; 

 buccal cavity ovoid and contains a spear. Sexual dimorphism well 

 marked. Male cylindrical and without bursa. Female globular, 

 with symmetrical uterus. Metamorphosis complex. 



Cobb (1902) states that Heterodera is similar to the genus 

 Tylenehus in many respects, but differs mainly in the complicated 

 metamorphosis which takes place in Heterodera. It also differs 

 in that Heterodera possesses two testes in the male, species of 

 Tylenehus possessing only one. 



Two species of the genus Heterodera have so far been estab- 

 lished, viz., //. schachtii parasitic more especially in the sugar 

 beet, and //. radicicola (Greef Muller), which has a much more 

 widespread distribution and a greater range of host plants. From 

 the development of the parasite described in this paper the 

 organism undoubtedly belongs to the Heterodera. The table 

 presented below is a modification of one given by Bessey that 

 has been slightly extended to include features not given in the 

 original, and at the same time gives a comparison with the 

 organisms under investigation. It will be seen that there are 

 certain substantial points of difference which, in my opinion, 

 cannot be ignored. Some of these appear to be intermediate 

 between the distinguishing features of II. schachtii and II. 

 radicicola and the question arises whether the organism in the 

 potato can be regarded as a new species or whether, knowing that 

 Heterodera is a plastic organism exhibiting numerous small 

 variations, we are to look upon our organism as an extreme 

 variety resulting from environmental difference and consequently 

 not of specific rank. Up to the present time I have not been 

 able to procure //. schachtii for comparison, as this species has 

 not been obtained in South Africa, and so I am disinclined to 

 pronounce any definite views. We must regard the parasite as 

 //. radicicola, and take the view that differences such as the 

 number of eggs, their size, and whether they are deposited by 

 the female or not, can be reconciled with normal variation. 



The table of comparison is as follows: — 



