to associate with a species that enters its host by penetrating 

 the body wall. 



After arriving in the body cavity of the host the larval nema- 

 todes grow rapidly and development is usually so timed that 

 females copulate and deposit eggs before the fly pupates. 

 Adult flies were found that contained egg-laying female nema- 

 todes and also small larvae that approximated the size usually 

 reached after a few daj-s of parasitic life. Hungerford believed 

 these small individuals had been arrested in development by 

 the growth and maturity of the other worms. 



Eggs pass through the vulva and are retained within the 

 separated but unshed cuticle of the final molt which, near the 

 middle region of the body, becomes distended to form a more 

 or less spindle-shaped egg capsule (Fig. 1(58 H). Eggs are not 

 normally discharged from this capsule prior to the death of the 

 female. This final molt of the female is the only one men- 

 tioned by Hungerford. How the males circumvent this encom- 

 passing cuticle and effect coition is not explained. The host 

 insect is eventually killed and the body disintegrates to set free 

 a residual mass of nematode eggs. 



Hungerford found that the internal fat deposits of infected 

 fly larvae were largelj' consumed leaving the body much more 

 transparent than that of a normal individual. Most infected 

 fly larvae died before pupating but where the infection was 

 acquired late or the parasites were few in number the fly might 

 endeavor to pupate. Many such pupae died being little more 

 than nematode-filled shells but some succeeded in casting off 

 the larval skins. The emerging, infected adults were able to 

 fly and differed very little in appearance from normal indi- 

 viduals but they lacked functional reproductive organs. 



Aproctonema entomophagum Keilin, 1917, was found in 

 England where it is a parasite of the dipterous insect, Sciara 

 pulhda Winn., the larval stages of which inhabit decaying wood. 

 The morphology and life history of the nematode are discussed 

 in a paper by Keilin and Robinson (1933) upon which the fol- 

 lowing account is based. It will be noted that the host of this 

 parasite belongs to the same genus as the host of Tctradonema 

 plicans and the two nematodes have many points in common. 



Each infected larval fly usually harbors several females of A. 

 entomophagum (Fig. 168 F) and a varying number of smaller 

 males (Fig. 168 E). Mention is made of one larval fly that 

 contained 2 females and 10 males. The parasites reach ma- 

 turity in the body cavity of the host and copulate whereupon 

 the males die and the females emerge forcing their way out of 

 the host in the manner of most mermithids. Egg laying begins 

 almost immediately after emergence. Each female deposits 

 somewhat over 200 eggs and when egg laying is completed the 

 female dies. Hence only the female has a free-living, post- 

 parasitic stage and it is of very short duration. 



The egg (Fig. 168 A) is laid before cleavage but develops 

 rapidly and in a few days contains a coiled larva (Fig. 168B) 

 that molts before hatching. There seems little reason to doubt 

 that the larval mermithids enter the young fly larvae by pene- 

 trating the body wall though actual penetration was not ob- 

 served. 



If infection occurs late in the development of the fly larva 

 the parasites may be carried through the pupal stage and in- 

 fected adult female flies were found though not infected adult 

 males. The parasites delay the metamorphosis of the insects 

 and infected adult female flies lack functional reproductive 

 organs. 



Paramermis contorta (Linstow, 1889) Kohn, 1913, is one 

 of the aquatic mermithids of which there are a considerable 

 number. It is a parasite of Chironomus larvae and was dis- 

 covered and studied in Europe. Each host usually harbors one 

 parasite but sometimes two to three or more. The sex ratio, 

 as reported by different investigators, varies a great deal but 

 in most cases females have considerably outnumbered males. 



According to Kohn (190.5), P. contorta molts before leaving 

 its host. This, undoubtedly, is the last molt and the uteri are 

 already filled with eggs. The parasite may issue through the 

 anus or force its way directly through the body wall, the ma 

 .iority emerging just before their insect hosts would normally 

 pupate. The worms settle into the mud at the bottom of the 

 pool and copulation soon takes place tg be followed immediately 

 by egg laying. According to Comas (1927), the uteri are emp- 

 tied and egg laying completed in 4 or 5 days whereupon the 

 female dies. 



Eggs are laid before cleavage but develop immediately and 

 hatch in the course of a few weeks. The mermithid larvae swim 

 in the water and seek young Chironomus larvae which they en- 

 ter by penetrating the body wall. Comas states that these 

 mermithid larvae do not appear capable of living long in 

 water and, if unable to find and enter a host, will die in a few 

 hours. Comas recounts that if a mermithid larva attempts to 

 penetrate between the more posterior abdominal segments of 

 its prospective host, the Chironomus larva may reach back and 



with its mandibles pull the nematode away or bite it in two. 

 If penetration is attempted nearer the middle of the body the 

 insect will be unable to reach the nematode and penetration is 

 more likely to take place. 



Allomermis myrmecophilia (Crawley and Baylis, 1921) 

 Steiner, 1924, was named and described by Baylis and its life 

 history was studied by Crawley (Crawley and Baylis, 1921). 

 The specimens were from two species of ants collected in Eng- 

 land, Lasius alienus (Fijrst), and L. flavus (F.) and a third 

 ant, L. niger (L.), was reported as a host. Observations on a 

 mermithid identified as this species and secured from the same 

 ants were made in Germany by Gosswald (1929; 1930). 



After completing its parasitic development this mermithid; 

 according to Craw-ley, emerges from the ant, sometimes through 

 the anus and sometimes between two of the ventral plates of 

 the gaster, whereupon it enters the soil. As with many other 

 mermithids, emergence apparently occurs over a considerable 

 period during summer and autumn ; Baylis mentions specimens 

 that emerged during July. Crawley first saw eggs in the uteri 

 of experimentally reared females on December .5. Egg laying 

 begins before completion of the final molt and many eggs are 

 retained within the separated but uncast cuticle after the man- 

 ner of Tetradoncma plicans. As mention is made of four ex- 

 perimental females that had molted by November 20, one might 

 infer that two molts take place after emergence but Crawley 

 and Baylis are not explicit on this point. Some of Gosswald 's 

 (1930) ant-infecting mermithids molted twice after emergence 

 Init presumably these were not A. myrmecophilia. Bj' actual 

 count Crawley found that one cast cuticle contained 6,560 eggs 

 and another 5,900 eggs. Oviposition continues after the cuticle 

 is cast off and probably at least as many more eggs are laid 

 making a total egg output of 12,000 or more. Eggs (Fig. 

 16S I) are embedded in a "gelatinous" matrix that causes 

 them to collect in masses around the vulva or sometimes to be 

 extruded in tlie form of a ribbon. Crawley and Baylis failed 

 to find males of this mermithid and Gosswald demonstrated that 

 females develop and lay viable eggs without copulation. 



Crawley believed that ants become infected while in the larval 

 stage and Gosswald 's infection experiments seem to indicate 

 that eggs of the parasite are ingested. Crawley and Baylis re- 

 ported finding only mermithogynes which, when present in a 

 colony, rarely exceeded the normal females in number and usual- 

 l.y were much fewer. One series of colonies showed an average 

 proportion of about 1 to 12. Gosswald found infected males 

 and workers of Lasius alienus and L. flavus and one infected 

 male of L. niger. Each infected ant usually harbors one mer- 

 mithid though sometimes as many as three. 



Infected males and workers, according to Gosswald, show, at 

 the most, only very slight external differences from normal ants. 

 The ovaries and wing muscles of mermithogj-nes fail to de- 

 velop normally, according to Crawley and Baylis, but, except 

 for a marked reduction in the size of the wings and a more 

 distended gaster, the external characters show no pronounced 

 dift'erence from those of normal females (Fig. 169 C & D). 



Hbxamermis sp. This unidentified species of the genus 

 Hexamermis is a parasite of the ant, Pheidole pallidula (Nyl.), 

 and its life history was studied in France by Vandel (1934). 

 Most individuals complete parasitic development by late summer 

 or autumn and emerge from the ant by forcing their way out 

 through the anus. They do not remain in the ant galleries but 

 penetrate a short distance into surrounding soil where they oc- 

 cupy small cavities. The final molt occurs about a month after 

 emergence and is followed, within the next month, by copula- 

 tion and egg laying. One of Vandel 's experimental females had 

 begun to lay eggs by December 23 and was still laying eggs on 

 March 15. Females exhaust their reserve nutrient materials, 

 stop laying eggs, and die by the end of March or soon there- 

 after. Hence there is one generation each season with no post- 

 parasitic individuals in the soil during late spring and early 

 summer. 



The infected individuals of this ant are mermithergates and 

 mermithostratiotes and, with at most very few exceptions, each 

 harbors one parasite. It is not known how the parasite enters 

 the host. Vandel concluded that the infection is acquired either 

 immediately prior to, or during the pupal stage. The location 

 where eggs are laid, the small number of parasites per host, and 

 the vestigeal caudal appendage of the adult is circumstantial 

 evidence suggesting that the larva penetrates the body wall of 

 the young ant. 



Copulation is necessary in the reproduction of this mermithid. 

 Experimental females reared in the absence of males by Van- 

 del failed to lay eggs. These females lost their opaque appear- 

 ance very slowly and some lived for from 22 to 33 months after 

 emergence whereas females that were allowed to copulate and 

 that layed eggs lost their opaque appearance much more quickly 

 and lived for only about 5 months after emergence. 



Agamermis dbcadbata Cobb, Steiner and Christie, 1923, oc- 



254 



