encyst in the mesentery. This was observed to occur when 

 a parasitized guppy was fed to a black bass. In all cases 

 the worms retain the cuticular "lioring tooth" until the defin- 

 itive host is reached, although three lips can be seen under 

 the cuticles in older larvae. Natural infections with similar 

 worms were found in several species of fish in Illinois. Sexual 

 maturity is reached only in birds. Fledgling cormorants be- 

 come infected when fed on infected guppies. The larvae at 

 first penetrate into the glands of Lieberkuhn, and when 

 fish are present in the ventriculus the.y leave the glands and 

 l)enetrate into the food during its digestion. 



Kahl, 1936, investigated the life cycle of Contracaecum 

 clavatum and concluded that it can undergo partial develop- 

 ment in a great variety of intermediate hosts, including Sagitta, 

 Calanidae, amphipods and medusae among invertebrates, and 

 in Ammodytcs and Mcrangiis among fishes. Wiilker, 1!)29, 

 thought there was a succession of three hosts, — plankton, plank- 

 ton-eating fish, and piscivorous fish, but Kahl thinks that all 

 three hosts are not necessary; development to the stage in- 

 fective for the definitive hosts can take place directly in such 

 fish as Merlangux merlangus. Merlangiis can also serve as a 

 definitive host, if infective larvae are swallowed Avith the 

 flesh of smaller intermediate hosts. 



Markowski (1937), influenced by Wiilker's work, found 

 that certain species of eopepods served as first intermediate 

 hosts for C. adinicum, and presented evidence for the view that 

 a variety of plankton-eating or carnivorous fish might serve 

 as second intermediate hosts, although he expressed doubt 

 that the larvae developing in the parenteral organs of a fish 

 would develop to maturity in the intestine of tlie same fish, 

 even if it were a suitable host. Markowski did not con- 

 sider the possibility of a plankton host being unnecessary. Ac- 

 cording to Kahl the larvae undergo their early development 

 in the intestine of the intermediate hosts, and then, when 

 about 5 mm long, acquire a boring tooth and penetrate into the 

 body cavity where they molt again, but retain the sheath 

 with tooth and posterior spine until eaten by the final host. 

 Essentially then, the life cycle of this species is similar to that 

 of C. spicidigeriim, although according to Kahl the eggs de- 

 velop embryos only after being swallowed by a host. For a 

 species living in marine hosts this might be necessary. It is 

 probable that all the species of Contracaecum conform very 

 closely to the same pattern. 



Thomas (1937c) worked out the life cycle of Ehaphidascaris 

 canadensis. The eggs of the species may become embryonated 

 after 8 hours outside the host and are infective within 24 

 hours, after one molt within the egg. When eaten by nymphs 

 of dragonflies, these eggs hatch, the first cuticle is shed, and 

 the larvae penetrate into the body cavity. Infected nymphs 

 caused infection in guppies, which in turn caused infection 

 in fingerling muskelunge. In Douglas Lake the livers of all 

 yearling Perca ftavesccns are full of Bhaphidaxcaris cysts, 

 whereas the plankton-feeding fingerlings are free of infection. 

 Guppies can be infected directly by the embryonated eggs, 

 the intervention of an invertebrate host apparently being 

 unnecessary, as in the ease of Contracaecum adiincnm. In 

 small bottom-feeding or nymph-eating fish, then, they become 

 encapsulated in the mesenteries and liver and continue growth 

 until eaten by species of Esox, in which the cycle is completed. 

 R. acus of Europe presumably has a similar cycle, since the 

 larvae are found in the inner organs of various cyprinoid, 

 salmonid and pereid fishes, whereas the adults are found in 

 Esox, Perca, Alosa and AnguiUa. 



The observation of Baylis on the probable relation between 

 Porrocaecum decipiens of seals and walruses and encapsulated 

 larvae in various fishes have already been mentioned. A num- 

 ber of European writers have reported encysted larvae of 

 Porrocaecum in insectivores (moles, shrews, desman) and 

 Schwartz (1925) has reported them from under the skin of 

 moles and shrews in the United States; he, and also Solonit- 

 zine, who has found the larvae of a Porrocaecum on the serous 

 surface of the stomach of a desman (Dcsmana moschata), 

 tliink the adult stage is probably reached in a bird of prey. 



Walton (1936a) found evidence for a similar life cycle for 

 Multicaecnm tenuicolle. Encysted larvae were found in spe- 

 cies of Sana and in Siren; 3 weeks after being fed to a young 

 alligator, presumably parasite-free, several immature males 

 and females were found. A similar cycle was found by Wal- 

 ton (1936b) for Ophidascaris labialopapUIosa; the larvae were 

 encysted in mesenteries and muscles of Sana spp., the adults 

 developing in Natrix spp. Similar larvae encysted in mus- 

 cles of Amphiuma, however, failed to develop in Natrix. Ort- 

 lepp (1922) failed to get larvae of O. filaria to penetrate the 

 mucous membranes when the ripe eggs were fed to a mouse, 

 although those of Polijdelphis anoura migrated to liver and 

 lungs like typical Ascaridinae. 



SPIRURINA 



Spiruroidea 



The members of this snperfamily, with a few exceptions, 

 show a striking degree of uniformity in the general features 

 of their life cycles. Although many species tend to live in 

 tlie walls of the alimentary canal or in more distant locations 

 in the body, the eggs, usuallj- embryonated, escape with the 

 feces, and usually hatch only after being eaten by an inter- 

 mediate host. The embryos of Habronema, however, hatch be- 

 fore escaping from the body. In most cases there is some 

 degree of specificity with respect to the intermediate host, 

 but usually it is not very close. After ingestion by the inter- 

 mediate host the first-stage larvae emerge from the egg, pene- 

 trate into the bodj' cavity or tissues, undergo two molts, and 

 become encapsulated as third-stage larvae. These larvae are 

 usually not sheathed, as are the larvae of metastrongyles; 

 the second cuticle is not needed as a protection, since this is 

 provided by a capsule produced by the host, so is completely 

 shed. 



Infection of the definitive host is nearly always by ingestion 

 of the infected intermediate host, although an alternative 

 method occurs in the ease of Habronema (see below). Not in- 

 frequently transport hosts may intervene between the true 

 intermediate host and the definitive host, and it is possible 

 that this can occur in all spiruroids. When the larvae are 

 eaten by a host in which the worm is unable to reach ma- 

 turity they burrow through the walls of the alimentary canal 

 and become reencysted. In most cases this seems to be an 

 optional course of development which is frequently favorable 

 to ultimate access to a definitive host (e.g., Spirocerca, Habro- 

 nema mansioni) but in the case of at least one species, Gnatho- 

 stoma spinigerum, a second intermediate host has apparently 

 become indispensable in the life cycle. After reaching the final 

 host the worms undergo two more molts before reaching 

 maturity. Being too large to enter blood vessels in the in- 

 testinal wall, they usually reach their destination, if this 

 is outside the alimentary canal, by direct migration through 

 tissues or along natural passageways. 



Gongylonema pulctirum will serve as an example of a typical 

 spiruroid life cycle. Gnatliostoma spinigerum and Draschia 

 megastoma will serve to exemplify two important variations. 



GONGYLONEM.\ PULCHRUM 



The adult worms live imbedded in the mucous membranes 

 of the esophagus, tongue and oral cavity. The eggs escape 

 into the lumen and leave the body with the feces in a fully 

 embryonated condition. No further development takes place 

 until the eggs are ingested by a suitable intermediate host. 

 This may be anj' of a large number of beetles, particularly 

 scarabaeids, or cockroaches. Twenty-four hours after inges- 

 tion by Btatrlla germanica, according to Alicata (193.5), empty 

 egg shells are found in the crop and intestine. The absence 

 of larvae in the lumen or wall of the intestine and the pres- 

 ence of a few still adhering to the wall of the crop, apparently 

 ready to invade the body cavity, suggests that hatching takes 

 place in the crop, and that the larvae find their way into 

 the body cavity by piercing the wall cf the crop. Forty-eight 

 hours after ingestion of eggs, first-stage larvae are found 

 in the body cavity, especially in the thoracic region. 



The newly hatched first-stage larva is cylindrical with a 

 spine and a small hook near the anterior end on the ventral 

 side, behind which about 20 rings of minute spines encircle 

 the anterior end of the body (Fig 190B) ; the tip of the blunt 

 tail is encircled by 8 to 10 small refringent points, a character 

 which is diagnostic of the first-stage lai'va. The filariform 

 esophagus and intestine are about equal in length. l)oth trans- 

 parent. The larvae wander about in the body cavity and grow 

 to double their original length in about 2 weeks, and at this 

 time are preparing for the first molt (Ransom and Hall, 

 1916; Alicata, 1935). The actual molt, according to Alicata, 

 does not occur until about the 19th day. 



The second-stage larvae lose the cuticular armature at the 

 anterior and posterior ends, which are bluntly rounded. The 

 slender esophagus occupies about one-half the body length, 

 and in older larvae becomes differentiated into an anterior 

 muscular portion and a posterior glandular portion. These 

 larvae increase in size to a length of 1.5 to 2 mm by the 

 end of the fourth week, when they liegin the second molt. 

 At about this time they usually penetrate the muscles of the 

 body wall, and sometimes, in heavy infections, other muscles, 

 and they may become partially encysted prior to the second 

 molt. 



Third stage larvae are found encysted at the end of about 

 a month. This stage is distinguished by a raised lateral bor- 



282 



