I. Du-i'YOrwi.is si'P, 



Tho ogRS of /'. filiiriii iiiiil l>. rni/xin/.v Iwitcli in tlie Inoiulii. 

 or at least in tlic iiitostino, as tlii'v aro loaviiiR the body of tin' 

 dotiiiitivo liost, Imt tliosi- of />. nrnfiilili, aiTiiidiiiu to Wi't/.il ,inii 

 Kiiigk (IS'.'tS) fail to liatoli in ttio UinRS, anil iisually do mil 

 liati-li nntil a few lionrs after leavinR tlie body. The first nioll 

 nsiially takes plaee at room temperature in from 1 to ;; days, 

 anil the seeond in from 3 days (in />. anifii'lili) to aliimt I'J 

 days (P. filaria) later, t'snally both sheaths are present in 

 early third stage larvae, but the lirst eutiele is eventually lusl. 

 These infeetive larvae live a long time in moist soil or water, 

 and .-ire able to survive in earthworms if eaten by them, al 

 though they do not depend upon the earthworm as an inter 

 mediate host. The use of earthworms as transport hosts seems 

 to be of less importnnee in the e.iso of Dictiincaidiis than in the 

 oa.se of Si/nflamux (see aboveK However, there is no evidenee 

 as yet that DirlnoftDiliix ean use as large a variety of transiiorl 

 hosts as ean Siinonmiis. 



'2. Mbri'ASTKON'CVI.US 



Mi'taslroiiffjiiu.i ilontiatiui (= apri), M. .salmi, and Chornt 

 .ilrotiffiilii.t pudcndotictii.i. The eggs of these worms eontain 

 fully developed embryos when deposited. .\lthinigh usn.-illy 

 stated to liateh in the bronchi or intestinal tract during passage 

 out of the definitive host, Alieata (10.S.">) found that they are 

 usually passed in the feces unhatched, and remain unhntehed 

 until taken into the bod.v of a susceptible intermediate host. 

 The eggs or embryos nia.v, however, remain viable for '.i months 

 in moist soil. 



When ingested by earthworms (species of Jlrloilriliis ,iiul 

 I.iimbricus) the larvae burrow into the walls of the esophagus 

 and proventriculus of these hosts. Alieata has found them there 

 K! hours after exposure to infection. They also enter the 

 circulatory system and may be found in the hearts, but 

 Schwartz and Alieata (1!)2!0 showed that migration via the 

 blood stream was not an essential part of the life cycle of this 

 worm in its intermediate host. In the earthworm the first molt 

 occurs about 8 to 10 days or more after infection, and the 

 second one a few days later, this molt beginning before the 

 first cuticle has been shed. The seeond cuticle is retained by 

 the third .stage larvae, which are now infective. The larvae do 

 not si)ontaneou.sly leave the host, and an earthworm may re 

 main infective over winter, and probably at times for several 

 years. Upon death of the earthworms the larvae are able to 

 survive for 2 weeks in moist soil. Pigs become infected by 

 eating infected earthworms or liberated infective larvae. After 

 ingestion, according to Hobmaier and Hobmaier (li)29), they 

 migrate via the lymphatics or blood stream, und rgoing the third 

 molt in mesenteric lymph glands, and then proceed via the 

 lymjihatic and blood .systems to the lungs, where they become 

 mature after a fourth .■ind final molt. 



?,. Pkotostrongvi.inak 



.Ml the members of the family Protostrongylinae resemble 

 one another in requiring molluscs as intermediate hosts. In 

 all cases the embryonated eggs hatch before leaving the body, 

 or soon after, and the first stage larvae may live in soil or 

 water for several weeks, but without further development. The 

 larvae are attracted by the slime of molluscs, and upon coming 

 in contact with a mollusc they creep into furrows in the foot, 

 whence they penetrate into mucous glands, burying themselves 

 in the muscular connective tissue under the e])itheluni. Here 

 they coil up and soon become enclosed in a tubercle resulting 

 from encapsulation by the host. The fir.st molt usually takes 

 place after a week to 10 days at room temperature, the larvae 

 having grown comparatively little in length, but having become 

 thicker. The second molt usually takes place in from 10 or 

 12 days (Aelurostrongylux, MiicUcriti.s, Crenosoma) to 4 or .t 

 weeks (Elaphostrongylus), after which the larvae are infective 

 when molluscs containing them are eaten. In most cases little 

 specificity is shown with respect to the species of molluscs 

 utilized as intermediate hosts, although, possibly because of 

 the habits of the snails, certain species seem to be of prime 

 imjiortance. I'mtdstroiij/i/liis riifisccns develops primarily in 

 Ilelicella (Hobmaier and Hobmaier, 1930) ; Miiellfriiis capil- 

 larix can utilize a great variety of snails and slugs, :ilthuug]i 

 Pavlov (1937) found only Ilelicella obxia to be important in 



Fig:. IH.-, DEVELOPMENT OV l'R( ITOSTKdXi; Yl.I X AE IN 

 MOLLU.S(.'S 



Larvjte of MueUerUi^ capiUnris in AgrUtlimtix aurfittiH. X — Larvae in 

 furrow of foot of mollusk a few hours after infection; B — On first 

 day of infection (sagittal section); C — Coiled larva in foot on second 

 day of infection (horizontal section) ; D — I^arvae in sole of foot on 16th 

 (liiv of infection. .After Hobmaier, 1934, Ztschr. f. Parasitenk, v. 6 (5). 



.Jugoslavia; Aelumstrongyliis abstriistis, reported by Cameron 

 (1927) to utilize mice as intermediate hosts, apparently er- 

 roneously, according to Hobmaier and Hobmaier (1935) devel- 

 ops in a variety of snails and slugs, but Epiphragviophora 

 proved most suitable. Other forms in which a variety of mol- 

 luscs have been shown to serve as hosts are Aelurostrongi/liis 

 fatcifonnis (Wetzel, 1938), Crcnonoma viilpis (Wetzel and 

 Miiller, 1935), and Elaphostrongylus odocoilei (Hobmaier and 

 Hobmaier, 1934). 



Hobmaier (1934) believes that the utilization of molluscs as 

 intermediate hosts by the Protostrongylinae grew out of the 

 habit of the larvae of seeking protection from desiccation in 

 the slime of the molluscs. This predilection for slime extends 

 to the period of passage through the colon of the definitive 

 host, for the larvae are commonly found burying themselves 

 in the intestinal mucus and thus becoming located on the sur- 

 face of fecal pellets instead of iuside. In this position those 

 larvae which were not protected from desiccation by the mucus, 

 and subsequently the ti.ssues, of snails would fail to survive. 

 The larvae, as Hobmaier points out, differ widely in their 

 habitat in the snail from the parthenitae of flukes, which prob- 

 ably develop in snails because these were ancestral hosts. 

 Whereas fluke parthenitae are true internal parasites of mol- 

 luscs, lungworm larvae are scarcel.v more than external para- 

 sites. Larvae ingested by snails usually pass all the way 

 through the alimentary canal and fail to develop. 



277 



