F. H. Stewart 
167 
in that situation. An older larva (Fig. 19) measured 0-465 x 0-02 mm. (a 23), spear again 
0-012 mm.; it was found in the tissue of a leaf of a groundsel on the 5th day after infection, 
together with larvae measuring 0-25, 0-3, and 0-32 mm. Being thus associated with recently 
hatched larvae it was probably derived from an egg laid within the previous five days in 
a leaf axil of the plant. In both the 0-22 mm. and the 0-465 mm. larva the oesophageal bulb 
was distinct; the intestine (Figs. 17 and 19, OS) commenced behind the bulb at a distance 
equalling head to bulb; the alimentary canal was patent. 
A still older larva (Fig. 16) measured 0-65 x 0-018 mm. (a 36); spear still 0-012 mm.; 
the salivary gland ( SG) was apparent, with five nuclei of which the anterior probably forms 
the duct; the gland was situated further back than in the adult, the whole of it lying behind 
01; the nerve ring ( N ), and the two large nuclei of the posterior collar ( CN ), were also 
apparent, the latter as two black dots which I at first took for eye spots; the excretory pore 
was in the same situation as in the adult. The rudimentary vulva was situated three-quarters 
of the body-length from the head; it lay in a clear area in the midventral line, which re¬ 
presented the rudiment of the vaginae. This specimen was found in a leaf of a groundsel, 
ten days after infection, together with adults and other larvae. A young female (Fig. 20), 
from the same leaf, was probably also hatched in the same situation, not more than ten 
days previously; it measured 0-8 x 0-022 mm. (a 36). 
The outstanding fact in this specimen was the condition of the developing 
genital ducts, the vulva and the posterior vagina only being present, the latter 
already containing spermatozoa! The rudiment of the ovary was not observed, 
but there was no trace of germinal cells at the fundus of the vagina; a condition 
of protandrous hermaphroditism was therefore not present, such as occurs in 
Rhabditis (Leptodera ) (Schneider, 1866, p. 316). 
Length of time required for embryonic and larval development , and by one 
generation from egg to egg. 
We have seen above that recently hatched larvae, measuring 0-25-0*46 
mm., have been found in the leaf of a plant exposed to infection for only five 
days, older larvae, 0-65, and young adults after only ten days. We may there¬ 
fore conclude that embryonic development does not occupy more than five 
days, complete embryonic and larval development not more than ten, and 
that a generation from egg to egg could be completed in fourteen days, the 
conditions of temperature being those of a European spring, summer or 
autumn, with the day temperature not falling below 15° C. (60° F.). This 
agrees with the observations of Ritzema Bos (1892) on Tylenchus dipsaci 
(devastatrix) Kiihn. As in this species, and in contrast to T. tritici, many 
generations can thus succeed each other in the course of one year, enormous 
multiplication may occur in a short period. 
Figs. 15, 16. Aphelenchus phyllophagus n. sp. Specimens from Senecio vulgaris. 
Fig. 15. Egg from leaf axil, 28th day. Outline. 
Fig. 16. Larva, 0-65 mm., from mesophyll, 10th day. 
Fig. 17. Larva, 0-22 mm., from leaf axil, 28th day. 
Fig. 18. Egg from leaf axil, 28th day. 
Fig. 19. Larva, 0-465 mm., from mesophyll, 5th day. 
Fig. 20. Young female, 0-8 mm., posterior third of body, from mesophyll, 13th day. 
