23 



nematode which attacks the sugar beet does not form galls such as 

 we meet with here, but the females locate so near the surface of the 

 root that in their increase in size they rupture the epidermal tissues 

 and their posterior portions project into the soil, whence, according 

 to Strubell, they are fertilized by the males. In our form, however, 

 while some of the females are located near enough the surface for 

 this to be possible, most of them are completely imbedded in the 

 tissue of the gall, through which the male must penetrate in order to 

 reach them. After copulation the male perishes and the female con- 

 tinues to develop. It still increases somewhat in size and in about 

 five or six weeks from the time it entered the root it reaches its 

 mature form shown in plate IV., fig. 6. It is now about i mm. (75^5 of 

 an inch) long and more than half as broad, being visible to the 

 naked eye as a little white pearl-like speck or globule in the tissue of 

 the gall. It still retains the spear andoesophagal bulb, but the intes- 

 tine is disorganized and indistinguishable. The body cavity is filled 

 with fat globules which render it semi-opaque. In the most trans- 

 parent specimens the ovary can be somewhat distinguished, consist- 

 ing of two long tubes coiled about in the body, filled with eggs in 

 various stages of development and uniting at the sexual opening at 

 the posterior end of the body. Plate IV., fig. 7, shows the ovary 

 removed from the body by crushing it open. The extremities of the 

 two tubes are filled with a transparent mass of small cells, the undif- 

 ferentiated eggs. Below this the eggs become more and more 

 mature, developing fat globules and a very prominent nucleus. Fer- 

 tilization takes place in the ovary tube so that the eggs located 

 toward the opening are partly developed. Life becomes extinct in 

 the female at the time when the eggs mature and there remains 

 simply a cavity in the gall filled with eggs, young worms, and the 

 remains of the old one. The young worms gradually find their way 

 out into the soil, seek new roots to attack, and a new generation 

 begins. 



Recapitulation of the Life History of Heterodera and the Formation of its 



Galls. 



Let us now briefly review the course of development of this worm 

 and the galls which it produces. Young worms coming into the soil 

 from previously affected plants wander about until they find roots 

 suitable for their attacks. Aided by a spear-like organ in the head 



