tie. ixa. 



Aitcnris tttitnn. Liirva in sfctinn of iiinu.-t' lung 1 VM-t'k iiflt'i" iiifei'tiori. 

 AftiT ISansoiii. 1!)20, U.S. 11. A. Yeailiook. 



this louto, :iiiil souu' aio luolmlil.v ]pii-kc'il \ii> :ni(l cniicd h.v 

 the circulatoiv system. 



Axcarus Iinnbricoide.s. Long: tlimij^lit Ui liave a liireet devel- 

 opment in the intestine, Ascari.s Iiiiiibricoidi's was fiist shown to 

 undergo a preliniiiiaiy migration tluough the body by Stewart 

 (1914) ; Stewart found that eggs fed to rats migrated to the 

 lung.s, and erroneously concluded that rats served as intcrmedi 

 ate hosts. Shortly thereafter Ran.som and Poster (1917) and 

 Chandler (1918) called attention to the probability that the 

 migration through the body was a part of the normal develop- 

 ment in the definitive host; experimental proof, with details 

 of the development, was supplied by Hansom and Foster in 

 llliO. Details of the course of the migration were worked out 

 and reported by Ransom and Cram in I'.l'Jl, and further details 

 were supplied by Roberts (lil34). 



The first-stage larva appears in the egg on about the eighth 

 day at the optimum temperature of HO to 33° C, and the first 

 molt occurs in the egg on about the ISth day. Ransom and 

 Foster (lifJO) fir.st observed that the embryo underwent a molt 

 in the egg. Later Alicata (1934) reported that the egg is not 

 infective until after this molt; he also pointed out that the 

 embryos of A-'scaridia lineata, Parascaris cqiionnn, Toxocara 

 canis, Toxa.scuris leonina, Heleral'is gaUinae and the roach 

 oxyurid Blatticola blattac also underwent a molt, a feature 

 which may be common in the Ascaridina and which determines 

 when the egg has reached the infective stage. 



Normally the eggs of Ascarii Inmbricoidcs hatch in the small 

 intestine after lieing swallowed, but they will sometimes hatch 

 when implanted subcutaneously or intraperitoneally (Ransom 

 and Foster, lfl20; Yoshida and Toyoda, 1038) or in artificial 

 media containing glucose or various nitrogenous substances 

 (Voshida and Toyoda, I.e.). 



The second-stage larva has a small, sclerotized, knob-like 

 structure at the anterior end, called the "boring tooth." The 

 larvae bore into the intestinal wall, mainly in the duodenum 

 and upper part of the .je.iunum, after hatching; the ma.jorit.v 

 have disappeared within 2 hours. The ma.iorit3' enter the blood 

 stream after some hours and are found in the liver in from IS 

 hours to several days after infection. A few apparently enter 

 lymphatics since they are sometimes found in mesenteric lymph 

 glands, but from here they seem to go via mesenteric venules 

 to the liver rather than directly to the lungs. Within .t or 6 

 days all have left the liver and have gone to the lungs via the 

 blood stream; some appear in the lungs within 18 hours, and 

 they may continue to be found there for 10 or 12 days, al- 

 though most numerous on about the third to fifth days. Dur- 

 ing the first 2 days of this migration the larvae grow consider- 

 ably. About the fifth or si.^th day the larvae in the lungs, 

 measuring about 0.8 to 1 mm in length, undergo the second 

 molt. The third stage larva has three lips with papillae, l:icks 

 the boring tooth, has a highly developed muscular esojihagus, 

 has the intestiiuil cells packed with granules, has a distinct 

 nerve ring and oval genital primordium, and a conical tail 

 turned dorsad at the tip. 



On the tenth to twelttli days llie llni<l It occins, also in 



till' lungs. In the <ipinion of Roberts, althotigli second and 

 Ihiril stage larvae m.'iy be found in the intestine prior to the 

 tenth day (Ransom recovered larvae from the trachea as 

 early ;is the third day), these larvae have not completed their 

 development in the bmgs an<l probably fail to I'slablisli them- 

 selves in the intestine The suggesticui is made that the oc- 

 currence of such l;irvae in the intestine may indicate unfavor- 

 able conditions in the lungs resulting from excessive infections. 

 Roberts found some hundreds of fourth stage larvae in the in- 

 testine on the 14lh aiul 21st days, but no molting third-stage 

 larvae were fcnmd between the 11th and 14tli days. Fourth 

 stage larvae are 1.4 mm or more in length. The cuticle begins 

 to show striations, fin like lateral alae are present, the lips 

 resemble those of the adult, the esoyihagus is less bulbous, and 

 the sexes can be diflCrentiated by a difference in U'ngth of tail. 

 Rudimentary geiiilal tubules are present in the body cavity. 



.\fter arri\al in the intestine the larva grows enormously, 

 reaching a length of l(i to 2.") mm 2!) days after infection. Lar- 

 vae undergoing the fourth nudt measure 17.3 to 22.5 mm (Rob- 

 erts). The lateral alae have become inconspicuous, the genital 

 tubules and body wall muscles are comparatively well devel- 

 oped, and the cliaracteristic features of the tail of the two 

 sexes are present, (irowth to maturity and beginning of reju-o- 

 duction takes several weeks. 



It is obvious that the only striking difference between this 

 life cycle and that of the heterakids is the entrance into the 

 circulatory system when burrowing into the intestinal wall, the 

 consequence of which is the migration through the body via 

 liver, heart .and lungs. The determining factor seems to be the 

 age at which the larvae do their burrowing. Eiitcrobiiis and 

 Dermatoxys, as we saw, burrow as fourth-stage larvae, and 

 some species of Ilclnakis do likewise and live as adults in the 

 burrows; Ascaridia burrows while in the third stage; but As- 

 cari.i burrows immediatel.v after hatching as a second-stage 

 larva. The burrowing heterakid larvae are too large to enter 

 or be sucked into blood vessels, whereas the Asearis larvae can 

 easily do so. The failure of T()xa!icari.<i larvae to enter the 

 circulatory system except rarely ma.v be found to be due to a 

 difference in size, particularly in the diameter of the larvae. 



Toxocara canis has essentially the same life cycle as Ascaris 

 himbriroidrs, and the same is true of Neoascaris vitulorum 

 {vide Schwartz, 1922), of Parascaris equorum (vide Baylis, 

 1923), of A.'icaris coliimnaris (vide Goodey and Cameron, 1923), 

 and probably of all other A.scaridinae. According to Fiilleborn 

 (1921), Toxocara canis is frequently encapsulated in the tis- 

 sues of mice or other abnormal hosts, which thereby become 

 transport hosts. 



Anisakin.\e 



It has long been known that various members of this sub- 

 family occur as immature worms in the body cavity, mesen- 

 teries and other organs of various vertebrates, and sometimes 

 invertebrates, whereas the adults occur in vertebrates which 

 prey upon these hosts. Although morphological characters 

 often suggested affinities between larvae and adults there 

 was little experimental evidence in support of them. More- 

 over the various larval forms were not clearly differentiated 

 from each other. Baylis (1916) for instance, showed that a 

 number of larval forms were confused under the iianu' "Ascaris 

 capsnlaria," which he believed on moriihological and distri- 

 butional evidence to be the larval form of "Ascaris dccipicns" 

 (now Porrocaeciim tircipiens). The same confusion probably 

 holds for other species. 



Thomas (1937a, 1937b) experimentally worked out the life 

 cycle of Coiitracaccum spiciiligcriim. Eggs obtained from the 

 proventriculus of a cormorant contained active molted larvae 

 with a boring tooth after being incubated in water for 5 

 days, and on the sixth day they molted a second time and then 

 hatched. Many attached themselves by the anterior end of the 

 sheaths, which seemed adhesive, but the.v swam freely when 

 detached. On the thirfi-eiith day a third molt was in progress, 

 with a cuticular tooth still present. When swallowed b.v tad- 

 poles or guppies (.Lahislis rctici(hilits) the larvae shed their 

 sheaths and were found free in the intestine or in the body 

 cavity. About 3 months later larvae were found encysted in 

 the mesenteries; they had grown to 1.3 mm in length (from 

 less than 400 m). In cysts developed by the host tissues they 

 continue to grow until nearly adult size is reached. Unlike 

 most nematodes the number of molts is not limited to four; 

 as many as eight molted cuticles have lieen removed from en- 

 cj'sted worms from a natural infection. 



There is evidence that when ;in infected fish is eaten by 

 another fish the larv.-ie penetrate the intestinal wall and re 



281 



