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Parasitic Aphelenchi 
the glands in the dorsal sector; (3) Ascaris larva of the nineteenth day with 
glands growing from the dorsal sector into the two subventrals; (4) the great 
majority of adult nematodes with the typical three oesophageal glands. 
2. The Renette lies between the left lateral line and the intestine in 
Tylenchus similis Cobb (1915), and the three species under consideration. In 
the development of Ascaris lumbricoides, it originates in the same position, 
and thence gives rise to the apparently bilateral organ of the adult Ascarids. 
This origin of the excretory cell from the left lateral line is striking, and may 
prove to be of very general occurrence. Without laying too much stress on 
the homology, it may be recalled that the great, unicellular, skin glands of 
both lateral lines are the excretory organs of Cylicolaimus magnus Villot, 
Tlnoracostoma acuticaudatum Jagerskiold (Jagerskiold, 1901), and of the adult 
female of Oncholaimus vulgaris Bast. (Stewart, 1906). 
3. The Vaginae are derived, as we have seen (p. 167) from a super¬ 
ficial cell group, which gives rise to them only, and not to the remainder of the 
reproductive tube—the gonad proper. They are probably ectodermal, their 
walls are not endothelial, and their junction with the uterus is marked by a 
sphincter. The corresponding sphincter ig situated at the junction of the 
vagina and uterus in Cylicolaimus , Thoracostoma (Jagerskiold, 1901), and 
Oncholaimus (Stewart, 1906), in which genera the vaginae are much shorter 
than in Aphelenchus. In Cylicolaimus and Thoracostoma sperm is permitted 
to pass the sphincter, and the uteri function as receptacula; in Aphelenchus 
the vaginae are large enough to accommodate the whole sperm mass; in 
Oncholaimus, where sperm is not allowed to pass into the uterus, although the 
vagina is too small to contain it, the surplus is drained off into the intestine 
by the gonenteric canals (Stewart, 1906). 
The posterior vagina is the only portion of the posterior reproductive tube 
(of e.g. Tylenchus) which persists in Aphelenchus. 
IX. BIOLOGY OF THE PARASITIC APHELENCHI. 
The following experiments and observations were made principally on the 
species A. phyllophagus and olesistus. It may, however, be assumed that the 
three species are indentical in their general mode of life. 
A. Definitive habitat of the parasite. 
Aphelenchus fragariae. The strawberry plants received by Ritzema Bos 
(1891) were not fresh, and he was therefore not able to make satisfactory 
observations on the situation of the parasite. Marcinowski (1908) found them 
to be mainly ectoparasitic, in the leaf axils, and in the flowers among the 
stamens, during the month of May; only a few were endoparasitic, in brown 
patches of leaf sheaths. In June, however, they were chiefly endoparasitic, 
in leaves and stem. She notes that apparently healthy runners contained 
Aphelenchi in the bud. 
