HETERODERA RADICICOLA. 401 



Sometimes the slow-moving larva, having emerged from the egg 

 covering, is found to have penetrated the wall of the oviduct, and 

 is moving about freely in the general body cavity. 



The eggs are ellipsoidal bodies, usually symmetrical, but when 

 viewed from the side may appear slightly kidney-shaped. Their 

 size varies considerably even when taken from the same parent. 

 The average length of a batch of over one hundred eggs taken 

 from infested potatoes from Natal was found to be 92.4/x, and the 

 breadth 34.6/x. The length varied between the extremes of 



82.5/x and 115/x, and the breadth between 33^, and 36/j,. 



Eggs taken from potatoes from Potchefstroom : The average 

 size was 79/x long by 30/a bread, with a variation of length between 

 70/j, and 85/x, and of breadth between 24/x and 35jx. 



On one occasion exceptionally large eggs were taken from 

 a female worm in the roots of the Snapdragon (Antirrhinum), 

 one individual measuring 1 19/x in length and 43/x in breadth. 

 This great variation in size bears no relation to the stage of 

 segmentation attained by the egg at the time of measurement, 

 as might at first be imagined. Abnormally shaped eggs are occa- 

 sionally found; these, as a rule, being malformed in the uterus. 



The eggs are enclosed in a chitinous transparent covering. 

 Their contents are granular but small globules, apparently fatty 

 in nature, predominate. The nucleus can, as a rule, be easily 

 recognised as a relatively clear spot, centrally situated. Segmen- 

 tation proceeds regularly and almost equally. Polar bodies, two 

 in number, were observed. The morula stage is formed by about 

 thirty blastomeres, after which the gastrula stage is produced 

 by invagination or embole. After gastrulation, further multipli- 

 cation and segregation of the blastomeres occurs, until eventually 

 a vermiform embryo coiled into two or three loops within the 

 egg covering is formed. (Fig- 2.) A slow movement scon 

 commences within the egg, the embryo exerting much pressure 

 upon the egg covering. Although the "spear" in the buccal 

 cavity is already fully developed, the embryo does not utilise it 

 to pierce its way out, but an escape is eventually effected by the 

 egg "shell" rupturing at one end, and so liberating the larva. 



The eggs are usually found to the number of about sixty in 

 the gravid female. As a general rule they hatch while still located 

 in the dilated uteri, and the final escape does not occur until 

 after the parent's death. The worm consequently cannot be 

 regarded as oviparous, and at no time have I seen evidence of 

 egg laying; indeed this does not appear possible, because 

 the vaginal orifice of the female ceases to become prominent soon 

 after egg formation commences. With normal weather conditions 

 in Johannesburg five or six days was the period necessary for 

 the complete development of eggs isolated from the parent in a 

 glass container. 



The Free Living Larva. 



The larva (Fig. 12) on escaping from the egg measures from 

 345/j, to 370ja long, the average length being 358jx. The maximum 



