Water uptake and hatching in the potato cyst nematode, Heterodera rostochiensis, and the root knot nematode, Meloidogyne incognita.

1. The second-stage larva of the plant parasitic nematode Heterodera rostocfaensis shows very little movement while confined to the egg; on the other hand, the larva of the closely related Meloidogyne incognita is very active 2. Using interference microscopy, it is shown that the water content of the Heterodera larva increases immediately it is liberated from the egg while that of the Meloidogyne larva remains constant. 3. It is suggested that the Heterodera larva is physically constricted by the egg shell and that this restricts both its movement and its water content. 4. Measurement of larval and egg volume inbothforms supports this hypothesis. The Meloidogyne larva has about 30 % of free space inside the egg shell while the Heterodera larva fits it completely. 5. It is suggested that these differences can be correlated with differences in the distribution and life-history of the two forms.