(liT of the mouth and by four, occiisioiuilly only two, small 

 fligitiform processes on the tail. The larvae are found imbedded 

 within the sarcoplasm suriounding a niusfle fiber. As the 

 cysts become well formed they are sometimes pushed out into 

 the body cavity, remaining attached to the muscle by a thin 

 strand, or eventually falling free. Baylis (192(i) found that 

 the larvae would eseajie from disintegrating cockroaches into 

 water, and could be kejit alive for a number of days, Imt 

 since the larvae settle to the bottom he concluded that drinking 

 water was not an important means of infection. Freed larvae 

 were found to be incapable of skin penetration. The possibility 

 exists, of course, that larvae, either in or out of their inter- 

 mediate hosts, might reencyst in some transport host; Alicata 

 (I.e.) cites the finding of third stage larvae in the stomach 

 wall of a mole. 



Upon ingestion by a definitive host (Alicata used guinea 

 pigs for experimental infections) the larvae are liberated 

 in the stomach and may invade the esophagus within one-half 

 hour after feeding, entering through the tissue at the gastro- 

 esophageal junction. They migrate ujiward througli the epithe- 

 lium of the esophagus and may roach the tongue as early 

 as the third day. Larvae begin the third molt on the ninth 

 day after ingestion, and many fourth-stage larvae are pres- 

 ent by the twelfth day. These larvae are characterized by 

 development of the reproductive organs, gradual develop- 

 ment of the characteristic cuticular bosses at the anterior 

 end, and loss of the caudal appendages. The final molt oc- 

 curs about a month after infection ; the minimum time re- 

 quired for growth to maturity seems not to have been de- 

 termined definitely, but Ransom and Hall (I.e.) report the 

 finding of egg-bearing females in a sheep about 3 months 

 after infection, and Alicata (lilS-'i) obtained an adult male 

 70 days after infection. 



Gnathostoma spiniuekum 



The adult worms live in tumors in the wall of the stomach 

 of Felidae, or of the esophagus of mink, the eggs escaping 

 into the alimentary canal through ojienings which eventually 

 develop from the tumors into the lumen. The eggs escape 

 from the body in an early stage of development (one to two- 

 celled stage according to Pronimas and IJaengsvang, 1933; 

 one to many-celled according to Refuerzo and Garcia (1938). 

 In aerated water they become embryonated in a minimum 

 of about 4 or o days, and in 2 days or more thereafter the 

 embryos emerge from the egg in an onsheathed condition, 

 being, therefore, in the second stage. These larvae have 

 smooth cuticles devoid of spines or striations, and are armed 

 with a spine at the anterior end. 



The larvae usually live for only a few days in tapwater 

 (Prommas and Doengsvang, 1933) although sometimes they 

 may live for a month or more (Yoshida, 1934). Further de- 

 velopment is known to occur only when the larvae are ingested 

 by Cyclops. Attempts to infect mammals, fish, frogs, fleas 

 and Cladocera have all been negative. The development of the 

 larvae in Cyclops was independently discovered by Prommas 

 and Daengsvang (I.e.) in Siam and by Yoshida (1934) in 

 Japan. These workers showed that sheathless motile larvae 

 were found in the stomachs of Cyclops soon after experimental 

 exposure, and that by the following day they could be found 

 in the body cavity. According to Refuerzo and Garcia (1938), 

 the larvae in the liody cavity 1 day after infection lose the 

 sclerotized oral spine, and a tieshy enlargement representing 

 the future lips develops at the anterior end. Three days later 

 the cuticle becomes striated, its armature of spines develops, 

 and a head bulb armed with four rows of spines, and con- 

 nected with cervical sacs, is also present. The larvae seem 

 to have completed their development to the infective stage 

 by the sixth day. 



Attempts to infect cats by feeding them infected Cyclops 

 have been uniformly negative (Yoshida, 1934; Prommas and 

 Daengsvang, 1936) but Prommas and Daengsvang succeeded 

 in infecting a catfish, Clarias batrachus. The larvae were 

 found in the muscles of the stomach or intestine of the fish 

 2 to 6 days after infection and after 6 days or more they 

 were found, some free and some encysted, in body muscles. 

 Chandler (1925a) had reported the presence of numerous 

 gnathostome cysts in the mesenteries of Indian snakes, which 

 he found to undergo further development in cats (1925a) 

 until the adult morphology of Gnathostoma spinigerum was 

 reached (1925b) ; Chandler also called attention to reports 

 of probably identical larvae in pelicans and eagles. Subsequent 

 to the work of Prommas and Daengsvang many other interme- 

 diate hosts, natural and experimental, have been added, in- 

 cluding a considerable variety of fresh-water fishes, frogs, 

 and snakes. In all of these the larva undergoes considerable 

 growth, but does not develop more than 4 rows of spines on 

 the head bulbs, in contrast to the 8 to 11 found in the adults 



of Gnathostoma sphif/rnim. It is probable that the larvae al- 

 w^ays become encysted ultimately. 



Chandler (1925a) showed that when gnathostome cysts in 

 snakes are fed to cats they penetrate through the alimentary 

 canal and can be found parenterally within 2 days after in- 

 fection. Some are found free in the abdominal cavity, under 

 the parietal peritoneum, or in the capsules of the kidneys, 

 but the majority, and nearly all later in the infection, are 

 found burrowing in the liver. A single larva was also found 

 in the liver of an experimentally infected guinea pig. The 

 larvae in the livers of cats grow somewhat, and a vulva 

 and rudimentary genital tubes develop within (3 days. No 

 further development was observed in cats infected for as long 

 as 4 weeks, although in the meantime there was extensive 

 damage done to the liver. Subsequently (1925b) Chandler 

 found, in naturally infected cats, all stages of development 

 from (presumably) fourth-stage larvae burrowing in tine 

 liver, exactly like those obtained from exjierimental infectious, 

 to forms, still sexually immature, which had undergone the 

 final transformation to the adult morphology, and had 8 to 

 11 rows of hooks on tlie liead bulb, arid comiilcx spines on the 

 liody. Some of the worms which had undergone the final molt 

 were found still in the liver, but others were evidently migrat- 

 ing out of the liver; a few were found in the mesentery or 

 in the diaphragm, and several were in the stomach wall; 

 one was free in the .stomach. The worms in the stomach wall 

 were not yet enclosed in hard-walled tumors, Imt occurred 

 in submucous purulent cavities. It was evident from these 

 observations that the worms, upon gaining access to a defini- 

 tive host, migrate through the walls of the stomach or in- 

 testiiu> to the abdominal cavity and enter the liver, where 

 they burrow and feed actively for several weeks. They finally 

 enter the wall of the stomach from the peritoneal side, and 

 grow to maturitj'. 



Africa et al (193(ia) fed rats with encysted larvae and 

 found the larvae in the liver and body muscles 8 to 25 days 

 later. Infection of cats fed on gnathostome cysts from 

 cold-blooded hosts has been confirmed by Prommas and Daeng- 

 svang (1937), the prepatent period being 28 to 32 weeks, 

 and l)y Africa et al (193()b), who found semi mature worms 

 in tlie diaphragm and in nodules in the stomach wall nearly 

 4 months after infection. It is clear that the formation 

 of a tumor about the worms in the wall of stomach or esopha- 

 gus, which finally opens into the lumen, is a late stage of 

 development. It also seems evident from observations made 

 by the writer (1925b) that these tumors, when in the stomach 

 of cats, frequently become perforated into the peritoneum 

 and are then fatal. Yoshida 's observation that in luink the 

 tumors form on the esophagus in the lower part of the 

 thoracic cavity suggests that this may be the normal host and 

 habitat, and that in these circumstances there is less danger 

 of fatal parenteral perforation. 



Draschia meqastoma 



The life cycle of this worm is of particular interest since 

 it represents an intermediate evolutionarj- step from that 

 of the typical spiruroids to the filariae. It was first worked 

 out in detail by Eoubaud and Descazeanx (1921). 



The female deposits embryonated eggs in the alimentary 

 canal which, according to Roubaud and Descazeaux, hatch be- 

 fore leaving the body of the host. The first-stage larvae 

 possess a hooklike structure similar to the hook of Gongy- 

 loiiema, but the larvae are in a very immature state, the con- 

 tents of the body being granular in appearance, with no dif- 

 ferentiation. These larvae are ingested by young nuiggots of 

 flies, and there seems to be a fairly high degree of specificity. 

 Draschia megastoma and Habronema miiscae have been found 

 to be capable of development in a number of species of 

 Musca and also in Miisciim stabiilaiis and in Fannia, but ac- 

 tual transmission has been observed only in Musca domestica, 

 and was definitely found by Eoubaud and Descazeaux to fail 

 in the case of Muscina stabulans because of inability of the 

 larvae to escape from the proboscis of that species. H. micro- 

 stoma, on the other hand, develops primarily in Stomoxys, 

 but has been reijorted as developing in Sarcophaga, Lyperosia 

 and }[tisca as well, though Roubaud and Descazeaux (1922b) 

 state that it does not reach the infective stage in Musca 

 flomcstica. Development of Eabroncma larvae has also been 

 reported from Drosophila. 



The ingested larvae bore through the walls of the ali- 

 mentary canal of the maggots and enter the body cavity. 

 They live free in the body cavity for only a brief time, 

 and about the third day they penetrate into the Malpighian 

 tubules. Here they become quiet, and undergo the first molt 

 on the third or fourth day after ingestion. They lose the 

 oral hook, become immobile, and grow very thick and aausage- 



284 



