FREE-LIVING NEMATODES 



483 



6 (7) Esophagus with a distinct median bulb, and a more or less distinct 



posterior swelling. Males with bursa. . Tylenchus Bastian. 



Genus consisting of numerous species, many of them parasitic 

 in plants and sometimes highly injurious. Aquatic species are rather 

 uncommon. A single species found parasitic in a marine alga. 

 Principally owing to its economic importance the genus has a very 

 extensive literature. 



Representative species. . Tylenchus dipsaci Kiihn 1857. 



(-^ : 9 . .. = - ..-?'.. 9 ? . , 5mm . This species is found 



parasitic in onion and hya- 



(L. .-' . . . -, '? . -M . . 9 ? . . 1 4 mm. cmtri bulbs, and in a num- 

 vr* la \.ir- 1.9 2. ~\u her of other plants, and is 



very harmful. The spear, b, i, Fig. II, ishot forth by the muscles, 

 /, and is used to puncture the cells of the host plant. The spear is 

 tubular, and the juices of the host are sucked through the spear into 

 the intestine by means of the bulb, c. Often referred to in literature 

 as Tylenchus devastatrix. 



Habitat: Europe, America, Australia, and probably throughout 

 the temperate regions. 



FIG. 776. Tylenchus dipsaci. Kiihn. 



I, a female; II. head of the same more highly magnified; HI, tail of 

 a male; IV, view from below, of the female sexual opening; V, cross- 

 section of the neck passing through the median sucking-bulb; VI, front view 

 of the penes and their accessory parts; VII, cross-section through the middle of 

 a female, showing how the body-cavity is filled completely by the ovary (w) 

 and the intestine (z). 



a, lip region; b, tip of spear; c, median sucking-bulb; d, nerve-ring; 

 e, excretory pore; /. muscles for moving the spear forward; g, posterior 

 esophageal swelling; h, excretory gland; *', hind end of spear, three-bulbed: 

 j, loop in ovary; k, right spiculum; /, muscles for opening the vulva; 

 m, the vulva; 'n, glandular (?) bodies; o, bursa; p, hind end of ovary; 

 q, uterus containing spermatozoa and one segmenting egg; r, segmenting 

 egg; s. vagina; t, the vulva or female sexual opening; u, blind end of posterior 

 rudimentary ovary; , intestine, showing its cellular structure; w, cross- 

 section of an egg; x, anus; y, wings of the cuticula; z, cross-section of the 

 intestine. (After Cobb.) 



7 (6) Esophagus with only one swelling, corresponding to the median bulb of 



Tylenchus. Males without bursa. . . Aphelenchus Bastian. 



Genus consisting of numerous species, the majority parasitic in 

 plants, and often highly injurious. Some species parthenogenetic. 

 This genus closely resembles Tylenchus, from which it is distin- 

 guished by the absence of the bursa on the males, and by the less 

 developed posterior portion of the esophagus. This latter is so 

 deteriorated that it cannot be distinguished from the intestine. 

 The oral spear also is usually less strongly developed than in 

 Tylenchus, and its posterior extremity is less likely to present 

 bulbous swellings. As in Tylenchus, so here, some of the species 

 are known to revive years after having been dried up and con- 

 verted into "dust." In the dirt or dust adhering to seeds and 

 plants they are often transported long distances. Many of the 

 species, therefore, are now cosmopolitan. Like Tylenchus, this genus 

 has an extensive literature. 



Representative species. 



Aphelenchus microlaimus Cobb 1891. 



C_ : J . . ..*:....'?.... r^T 4 



U :!....',,.,?;, 



95.1 



--NI r 



' mm - Habitat: Douglas Lake, 

 Michigan. 



FlG. 777. Aphelenchus microlaimus. 



a, the lips; b, the spear; c, the nerve-ring; d, sucking-bulb; e, excretory 

 pore; /, ventral gland; g, blind end of testicle; h, intestine; *, cuticula or 

 skin; j, spermatozoon; k, right spiculum or penis; /, piece accessory 10 

 the spicula; m, anus; n, papilla; o, terminus. (After Cobb.) 



