96 JOURNAL OF THE 



ing. The ova begin to develop while the cyst is comparatively 

 small. Before the ovaries are fully developed they are capable 

 of a slight independent motion. Frequently in examining those 

 dissected from living cysts I have noticed a marked twisting and 

 tortuous motion, probably due to a contraction of muscles in the 

 walls. The body wall of the female is marked by irregular 

 transverse striae, but not so prominent as in the male. 



Length of Life Cycle. — This completes a life cycle of our 

 Heterodera i-adieiGola. It passes through all these changes, from 

 the devolepment of eggs, successively through the larval and 

 cystic state until eggs are again developed, in about one month. 

 This I was able to determine by watching the development of 

 the worms in the roots of "volunteer'^ potatoes which sprouted 

 about the first of October and were infected from the soil and 

 the "seed" potatoes. Thus in favorable seasons there would be 

 at this latitude seven or eight successive generations in a year. 

 Farther South, where the season is longer, probably the numl>er 

 of generations is increased. When we consider the number of 

 eggs one female is capable of producing, from one hundred to 

 two hundred or more, it will be seen that the worms multiply 

 with startling rapidity. The periods of transformation of dif- 

 ferent individuals do not altogether coincide, so that at almost 

 any season we may find worms in every stage of development. 



Brief Recapitulation of the Life History. — J£V/^ — 

 The oblong, bean-shaped egg, .08 mm. to .10 mm. long, devel- 

 oped in the anterior patt of the ovaries, after fertilization, enclosed 

 in a donble-wallod membrane, undergoes partial or complete seg- 

 mentation while yet within the uterus. From the l>eginuing of 

 segmentation to the fully developed larva five to seven days are 

 required. The thread-like larva is coiled three or four times 

 within the egg membrane. Larva — At the time of hatching or 

 soon thereafter it moults for the first time. It is "thread-like," 

 blunt at the head end and narrowly pointed at the tail end, .3 

 mm. to .4 mm. long. In the head end can be easily noted the 

 exsertile spear and the long, tortuous channel of the anterior part 

 of the oesophagus extending to a prominent ovoid or ellipsoid 



