to oat panicles, but, instead of eggs, deposit larvae of the nema- 

 tode parasite. These find their way, possibly in response to 

 some ehemotactic stimulus, into the plant tissues surrounding 

 the fly larvae." In this environment the nematode larvae con- 

 tinue development and two final molts take place, the last 

 cuticle separating while the larva is still within the cuticle of 

 the preceding molt. 



Larvae that Goodey removed fi'om the gut of infected flies 

 and kept in tap water completed their final molt in about 41 

 hours. Males remained alive for about 14 days and females for 

 about 29 days but copulation did not take place while the worms 

 remained in water. In nature copulation follows the final molt 

 and the uterus of the female is distended with spermatozoa. 

 The preparasitic female (Pig. 171 F & G) has a well devel- 

 oped stylet with basal swellings and a large dorsal esophageal 

 gland. These structures are inconspicuous or lacking in the 

 male. (Fig. 171 E). 



Tlie male does not again beconu- parasitic but the impreg- 

 nated, precocious female enters the body cavity of a frit-fly 

 larva. Goodey did not actually observe the entrance but as- 

 sumed, no doubt correctly, that it is accomplished by penetrat- 

 ing the body wall. The incidence of infection is about the 

 same for male and female flies except possibly in the grass or 



overwintering generation, where Goodey found that about two- 

 thirds of the infected flies were females. 



After becoming parasitic the female nematode increases very 

 greatly in size and is about fully grown when the host emerges 

 from its pupal ease. Tlie body has assumed the characteristic 

 "sausage shape" and the ovary has completed its development 

 (Fig. 11.') J, p. 136). The stylet is retained and Goodey be- 

 lieves that probably the parasite continues to take food via the 

 alimentary canal. 



Tylenchhicma oscincUae produces no noticeable effect on the 

 external characters of its host but it prevents the normal de- 

 velopment of the gonads and both male and female flies are 

 sterilized. Occasionally, however, parasitized flies of both sexes 

 develop normal sex organs and when this happens the parasite 

 fails to undergo normal development. In regard to this Goodey 

 (1931) writes: "In the great majority of cases the worm man- 

 ages to get the upper liand and grows to sexual maturity within 

 the host, but occasionally the fly, during its final metamorpho- 

 sis, is able, by some means, to Imild up its gonads in the nor- 

 mal manner. When this happens the worm fails to grow, re- 

 mains non-functional and becomes degenerate. . . . These rela- 

 tionships may possibly be explained on the supposition that the 

 worm secretes or excretes something, perhaps from the intesti- 



rig. 171. ALLANTONEMATIDAE 



A-G — Tylenchinema oscinellne (A — Very young male larva and, B, 

 genital primordium of same; C — Very young female and, D, genital 

 primordium and esophageal gland of same; E — Adult male; F — Adult, 

 preparasitic female and, G, anterior end of same. For fully grown. 



adult, parasitic female, see Fig, 115 J, p. 136). H-J — Allantonema 

 mil-able (H — Adult male; I — Adult, preparasitic female after copula- 

 tion ; J — Fully grown, adult, parasitic female. For stage intermediate 

 between I and J, see Fig. 115 I, p. 136). A-G, after Goodey, 1930; 

 H-J, after Wulker, 1923. 



il58 



