Most of llu'SO iioiiiatoilos :uo liisrwwil :iiul l'i'in;iU'.s inodiici' 

 fertile I'KKS only after eopulntioii. Males are usually somewhat 

 loss numerous than females, reaeh maturity a little quicker, 

 ami do not live quite so \o\\g. Aeeordiug to Johnson, females 

 of KhabdiU.i maiiimni usually, thouRh not always, reproduee 

 without males. In nmny speeies of this uroup a female may be 

 oviparous when young but toward the end of life sonio of the 

 last ecds produced may be retained and hatch in the uterus. 

 'Pile resultiiiR larvae may not escape thr(iii);h the vulva but un- 

 diTRo part of their development within the mother nematode, 

 eonsumiuf; her internal orjrans and convertint; her into a brood 

 sac. Incidentally, this same mode of reproduction is character 

 istic of many free-living species of Diplogastcr, Rhabdilix and 

 related genera. 



The sec(uid line of evolutionary development referred to above 

 may have been initiated when, during periods of adversity, cer- 

 tain sai'rophagous nematodes, seeking refuge and succor, en- 

 tered and temporarily dwelt within the bodies of other inver- 

 tebrates. In the case of nematodes in this category parasitism 

 apparently does not ordinarily result in the death of the host 

 nor are the parasites able to live in a decaying carcass. Usually 

 these nematodes either inhabit the alimentary tract of the host 

 (e. g., Aiuiiostoma limacis) or arc associated with its reproduc- 

 tive organs (e. g., " Angiostoma" hclicis). For at least one 

 species (i. e., AUoioncma appcndiciiJaUi) an alternation of one 

 or more parasitic generations with one or more free-living gen- 

 erations has become a more or less regiilar procedure. 



Rii.\BmTis M.\irpAsi Caullery and Seurat, 1919 (Syn. R. iiclUo 

 Butschli, 1S73; not Schneider, ISOG). Larvae of Shabtlitis 

 maiipasi are found in the nophridia and coelom of living earth- 

 worms. For Liimbricus terrcfitri.i L. the incidence of infection 

 is frequently very high and at least several and perhaps many 

 other species harbor these nematodes more or less frequently. 



Larvae are found near the uephridiopore in the dilated, muscu- 

 lar termination or "bladder" of the neiihridial tube. Often 

 nearly every tube is inhabited, the number of worms in each 

 varying from 2 or 3 to 12 or more. Also larvae may occasion- 

 ally be found in the seminal vesicles. When in these above 

 mentioned locations larvae are in an active condition and not 

 ensheathed. Johnson concluded that these inhabitants of the 

 neiihridia are not necessarily confined to this location through 

 out the life of the earthworm but may move out into the soil 

 and later go back through the nepluidiopores into the same or a 

 different earthworm. 



Larvae occur also in the coelom and these are usually en- 

 sheathed and inactive (Fig. 165C). Occasionally a larva may 

 be embedded in the muscles of the body wall or encysted on a 

 septum. Frequently several larvae are embedded in a brown, 

 oval body composed of cysts of the sporozoan. Monocystus, and 

 various earthworm tissues. Such bodies are most common at 

 the posterior end of the coelom. 



There is no evidence that the presence of these larval nema- 

 todes is detrimental to the annelid. So long as the earthworm 

 is alive the nematodes remain in a larval stage but when the 

 earthworm dies they quickly grow to adults (Fig. 165 A & B) 

 and reproduce in the carcass. Otter (1933) concluded that a 

 female lives from 7 to 10 days after reaching maturity and lays 

 from 150 to 300 eggs. Males, in his opinion, live about a third 

 as long as females. No doubt several generations occur before 

 the food supply is exhausted though Johnson was uncertain on 

 this point. After the body of the earthworm is consumed large 

 numbers of larvae move out into the soil where they live await- 

 ing the opportunity to enter another earthworm. Larvae from 

 the soil are said to be in the same .stage as those from the 

 nephridia, but what this stage is has not been stated. 



With regard to the method of entering the earthworm, John- 

 son writes: "Those that enter by the nephridiopores take up 

 their position in the terminal, bladder-like part of the nephridia. 

 Those that use the spermiducal apertures travel up the vasa 

 deferentia and occupy the seminal vesicles. Lastly, those that 

 pass in by the dorsal pores and the oviducal apertures find them- 

 selves in the coelom, where, being attacked by the amoebocytes, 

 they encyst. These encysted larvae coated with amoebocytes are 

 worked backward by the movement of the worm till they come 

 to rest in the tail end of the worm, where, together with other 

 foreign bodies, such as cysts of Monocjistix and discarded setae, 

 and with masses of dead brown-colored amoebocytes, they are 

 compressed and cemented into the brown bodies which are found 

 there." 



According to Keilin (1925) the accumulation of foreign bod- 

 ies in the posterior segment of an earthworm may induce the 

 development of a stricture that will sever this distended ter- 

 minal i)ortion from the rest of the body. The detached portion 

 then decomj)oses and in this manner M. maupnsi and other 

 coelomic j)arasites of the earthworm may be liberated. 



Males of E. maupasi are much fewer in number than females. 

 Although Johnson did not observe copulation, his rearing ex- 



periments lead him tu ccincluiii' that most females are lier- 

 ma))hro(litic but that occasionally females occur that are able 

 to reproduce only after being fertilized by males. Otter, who 

 observed co]>ulaticin and agrees, in the main, with Johnson, 

 writes that li. maupa.ii "may thus be considered to be one of 

 those species of Rliabdilis in which hermaphroditism is in a 

 very early stage, and in which funetion.al males, females, and 

 hermaiihrodite females, exist side by side in fluctuating pro 

 jiortions. ' ' 



I'Eu.sTiONCiiu.s AKRIV0K.\ (Cobb, 1916), was first found by 

 Merrill and Ford in the heads of termites, /.rHro/criiif.s- /»ci/».r/».s' 

 Rossi,* collected ne.ar Manhattan, Kansas. Under natural con- 

 ditions the nematodes varied from to about 75 per insect. 

 After experimental termites had been kept for 4 days in soil 

 heavily infested with P. acrivora, the average number of nema- 

 todes per insect was 46.0 while termites used as controls 

 averaged about 3 nematodes per insect. IIow the nematodes 

 enter or why, in living termites, they are found only in the 

 head are points that have not been determined. The parasites 

 do not reach nuiturity in living hosts but when the termites 

 are heavily infected they become sluggish and die, whereupon 

 the nematodes reproduce in the carcass. Hence, in this instance, 

 the relationship is not purely passive. 



Merrill and Ford were able to rear this nematode in water 

 cultures with various substances supplied for food, preferably 

 the macerated bodies of insects. Eggs hatched in about 18 

 hours and the adult stage (Fig. 165 .T) was reached in about 

 2 days. The complete life cycle from egg to egg required about 

 4 to 5 days but after beginning to lay eggs an adult female 

 usually lived for 12 to 13 days. During a period of 13 days 

 one female, while under observation, copulated with 7 males and 

 deposited 317 fertile eggs and 14 infertile eggs. Males were 

 somewhat less numerous than females. They lived for about 19 

 days and one male, while under observation, copulated with 10 

 different females. 



Toward the end of life a female becomes sluggish and eggs 

 are not extruded but hatch in the uterus. W'hile the resulting 

 larvae may sometimes escape through the vulva they usually 

 remain in the mother nematode, feeding on her internal organs. 



Since Merrill and Ford's investigations nematodes identified 

 as P. aerivora have been reported from various other habitats. 

 They have been found in other termites, usually located in the 

 head while the insect is alive. They have been found in dead 

 pupae of the corn ear worm, Hcliotliis armigcra (Hiibn.), and 

 in dead pupae of the rose leaf beetle, Kodonota puncticoUia 

 (Say). They have been found in grasshopper egg masses where 

 they were reported to have been destroying the eggs. On sev- 

 eral occasions they have been found in decaying plant tissues. 

 However, the populations from these different habitats may 

 represent different strains or, perhaps, even different, though 

 closely related, speeies. 



The peculiar habit of swallowing air, to which this nema- 

 tode owes its specific name, is shared by several species of Dip- 

 Jogastcr and Khabditis. When mounted in water on a micro- 

 scope slide, one of these nematodes may place its head against 

 the surface of an entrapped air bubble and air can be seen as 

 it passes down the esophagus to the anterior end of the intes- 

 tine where it is quickly absorbed. According to Cobb (1915) 

 some of these nematodes can ingest their own volume of air 

 in the course of an hour or two. The swallowing of air is ac- 

 complished by the usual rhythmic muscular movements of the 

 esophagus. During the first muscular movement a small bubble 

 of air passes quickly from the mouth to the median pseudobulb 

 where it stops. At the next muscular movement the bubble 

 passes on into the intestine while another simultaneously passes 

 from the mouth to the median pseudobulb. This may continue 

 uninterrupted for a considerable period of time. 



Neo.\plectan"a bibionis Bovien, 1937, was studied by Bovien 

 (1937) who found it in Denmark associated with the dipterous 

 insects Bibio ferruginatns (L.), B. hortidaniis (L.) and Dilo- 

 phim rtdgari.i Meig. 



An interesting and significant point in the life cycle of this 

 nematode is the occurrence of dauer larvae (Fig. 165 G). These, 

 according to Bovien, are in the third stage. A dauer stage is 

 not obligatory but occurs only when environmental conditions 

 arc unfavorable to enable the nematode to persist through pe- 

 riods of adversity. Dauer larvae are relatively sluggish and 

 are usually enclosed in a partly separated cuticle though this 

 may be lost before the end of the dauer stage. These larvae 

 are easily distinguished from third-stage larvae that develop 

 under favorable conditions being slenderer and differing in 

 other morphological details. Bovien found dauer larvae cling- 

 ing to the surface of adult flies and being transported by them. 



The various host insects become infected by swallowing these 

 dauer larvae which, on reaching the alimentary tract, remain 



*Regarded by Snyder, according to Van Zwaluwenburg (1928, p. 9), 

 as either Keliruliternie/t tibiaUjt Banks or R. claripennia Banks. 



247 



