228 ZOOLOGY. 



sickness is a nematode, of which the life history is 

 as follows. The female is found fixed to the branches 

 of the root; it is citron-shaped, about one twenty- 

 fifth of an inch long (Fig. 134, 1 and 10), and contains 

 on an average three hundred and fifty eggs. Some 

 few of these, together with a jelly-like substance 

 making up an " egg-sac," may pass out to the exterior, 

 but the large majority develop in the body of the 

 female, which ultimately becomes a mere sac enclosing 

 the eel-like larvse. The female is kiUed by the 

 process. The liberated larva (Fig. 134, 4) seeks out 

 a root (about one twenty-fifth of inch thick), and 

 bores into it. Here it lives as a parasite, causing 

 the disease of the attacked beet plant. The larva 

 quickly sheds its old skin, assumes a thicker form 

 (Fig. 134, 5), ceases to move, and gradually causes the 

 outer skin of the root to bulge out externally (Fig. 

 134, 3, a). The distinction between the sexes now 

 rapidly makes its appearance. A thick motionless 

 larva, destined to become a male, temporarily ceases 

 to feed, shrinks within its old skin, develops a thin 

 new one, and ultimately becomes a long eel-like 

 worm (Fig. 134, 6, 7, 8), which grows into an adult 

 male (8). In the stage represented in Fig. 134, 8, 

 the animal still lies under the outer skin of the root, 

 which never bursts during its development, but the 

 mature male bores out of its larval skin and out of 

 the root, passing into the soil, where it finds and 

 fertilizes the female, which in the meantime has 

 developed but remains attached to the root. The 

 female develops in a simpler way, by the gradual 

 distension and growth of a larva (not by a process 

 of re-formation) and gradual development of the 

 female sexual organs. As the larva passes from the 

 stage of Fig. 134, 5, into that of Fig. 134, 9, and 

 later on into the adult condition, 10, the outer skin 

 of the rootlet is ruptured, and the female comes out 

 from its tissues, remaining, however, attached to its 



