EELWOEMS. 73 



The Beet Eelworm (Heterodera SchacMii). 



For some time tlie beet crop on the Continent has been 

 seriously interfered with by a peculiar rotting disease, which 

 has been shown to be due entirely to the working of an eel- 

 worm, Heterodei'a SchacMii. The female is found fixed to 

 the root and rootlets of the beet, and, unlike most Anguil- 

 lulidae, it is citron-shaped, and seldom longer than ^th of an 

 inch : she nevertheless contains as many as three or four hundred 

 ova. The ova when laid are found in groups, being united by 

 a kind of gelatinous sac. The majority of eggs develop inside 

 the female, this process, as a rule, causing her speedy death. 



The larvae when liberated seek out a root of the beet and 

 bore into it, and here they live, causing the disease. When 

 they have entered the root they produce great swellings — 

 " galls," in fact — over their abode. The first form of larva that 

 has thus entered the plant sheds its skin, and instead of being 

 elongated it becomes thicker in shape, ceases to move, and lies 

 with the bulbous patch formed over it. At this time the 

 sexes commence to appear distinct. If the thick motionless 

 larva is to become a male it ceases to feed, shrinks within its 

 old skin, and develops a thin new one, very like the puparium 

 stage of some insects. The newly formed male worm inside 

 its old skin is more elongate — in fact, it resembles the typical 

 form of an eelworm. When mature this male bores its way out 

 of the root and commences its search for a female. Should the 

 larva become a female, the development is much simplified. 

 The female develops by a simple distension of the body and 

 the formation of the female sexual organs. There is no pro- 

 cess of reformation as we observe in the male. When the 

 female is fully formed, the lump on the root ruptures and 

 releases the worm ; but she, on the other hand, does not re- 

 linquish her hold of the plant, to which she remains permanently 

 attached. 



The development from the egg to the adult takes about 



