THE CAUSAL PARASITE. 27 



larv?e by the time they are laid. Whore this does occur it is mostly 

 only the last eggs produced and which the mother nematode has not 

 had the strength to force out against the large mass of eggs already 

 laid. In this the root-knot nematode differs quite markedly from 

 the sugar-beet nematode {Heterodera schachtii Schmidt), in which a 

 comparatively large part of the eggs produced remain within the 

 body of the mother and undergo segmentation and finally escape 

 from the shell, eventually escaping to tlie outside through the open- 

 ings in the body wall after the death of the old nematode. 



Segmentation of the eggs begins very soon in any case and proceeds 

 rapidly. It was not determined exactly how long the embryonic 

 development required, but it is apparently not over two or three 

 days in warm weather (much longer in cool). 



The eggs were laid at the rate of 10 to 15 a day in the cases 

 observed by the wi'iter, although in some cases egg laying may pro- 

 ceed even more rapidly. They are surrounded by a slimy or gelati- 

 nous substance, which incloses them and evidently acts as a pro- 

 tection. This is secreted by the nematode with the eggs, as was 

 observed on isolated mature females under the microscope. It 

 is at first quite liquid and colorless, but soon becomes rather firm 

 and light brown in color toward the outside. Tliis is the structure 

 that has been called by some investigators the egg sack (Eiersack); 

 for example, Voigt ^ and Strubell.^ The latter appHed the term to 

 the similar structure in the sugar-beet nematode (Heterodera 

 scliacJitii), and, erroneousl}', denied its occurrence in H. radicicola. 

 Occasionally the remains of the male may be found entangled in this 

 slimy mass. It is probable in such cases that after fertihzing the 

 female the male died and when the eggs were laid the egg mass sur- 

 rounded liis remains. The eggs at the outer portion of the mass are 

 usually either hatched or contain larvae, while those next to the body 

 of the nematode are not segmented. 



This egg mass is sometimes as large as the adult female and can be 

 seen readily when the latter partly projects from the root. 



LARVA. 



The larva (PI. I, figs. 3 and 4) emerges from the egg through a hole 

 which it pierces in the shell, usually at one end. It is a slender, 

 cylindrical animal, blunt at the anterior and tapering at the poste- 

 rior end to a pointed tail. The larvae when they emerge from the 

 egg are 375 to 500 /t in length^ and about 12 to 15 // in greatest 



1 Voigt, 1890. 



2 Strubell, 18S8. 



3 Stone and Smith (1898) give tlie lengtla of the larva as 350 u, but this is considerably less than the meas- 

 urements made by the writer. They give the egg length as 100 /t, showing that they were not dealing 

 with eggs helow the normal size. 



217 



