THE CAUSAL PAEASITE. 33 



The fully mature egg-laying female is of a glistening pearly 

 white color. The enlarged posterior portion is smooth and shows 

 no markings, except that the internal organs are visible where they 

 ap])roach the surface. The comparatively little enlarged anterior 

 portion shows faintly the transverse cuticular markings so charac- 

 teristic of the mature male. 



The bulk of the body of the sexually mature but not yet egg- 

 laying female is occupied by the enormously dilated ahmentary canal 

 (PI. I, fig. 11). The anus is a small round terminal opening, wliilo 

 the genital opening is a transverse slit slightly ventral to the anus 

 and bordered by two more or less well-marked lips. This opens into 

 a short, thick-walled vagina about 16 to 20 /i in diameter (including the 

 walls). At its upper end it is abruptly contracted into a tube 8 to 

 10 p. in diameter, which soon divides into two tubes, the uteri. These 

 are at first slender but slightly coiled tubes, leading forward (usually 

 lateroventrally) and gradually increasing in diameter. Just before the 

 ovary is reached each uterus expands into a spherical portion, about 

 16 /^ in diameter, apparently the receptaculum seminis. Above this 

 lie the cylindrical ovaries filled with the rudimentary eggs in the 

 form of a sort of parenchyma. At this time the whole reproductive 

 S3"stem if straightened out Mould not be more than 300 to 400 /i 

 long. After fertilization the uteri undergo a most remarkable elonga- 

 tion and become \&ry much coiled and tangled as they become 

 filled with the fertilized ova. Although the body of the nematode 

 increases rapidly in thickness, the increased space thus afforded is 

 not sufficient, the alimentary canal becomes pushed to one side, and 

 much of the space originally occupied by it is occupied by the uteri. 



Egg laying had already begun, in the earhest cases observed by 

 the wTiter, 29 days after the seed of the host plant (Pisum sativum, 

 the garden pea) in these experiments was planted in soil known to 

 be infested with the nematodes. Siace germination of the seed is 

 not immediate it is probably safe to assert that during warm weather 

 the period from the time the larva enters the root until it begins 

 egg laying is not over 25 days. This is somewhat longer during 

 cooler weather, i. e., in the early spring and in autumn. 



In most cases the greater part of the eggs are laid in an unseg- 

 mented condition. However, if the nematode is buried deeply in 

 the tissues so that their pressure impedes egg laying, the eggs may 

 develop and the larvae escape still wdthin the body of the mother, so 

 that the latter may be viviparous. The last few eggs often develop 

 in a similar manner, the nematode having evidentl}^ become so weak 

 that she could not deposit them before they underwent development. 



217 



