•<>r nsli from Citclopx a wcok aftrr iiifrctiim failod, pii'sumalily 

 hwaiisi' of iiia(lo<niatc timi" for tlio larvar lo ri'aili llio iiifi'ctivc 

 staRC. Fiiruyama ( I!i:f4l suci'ccilcii in cimipU'liiiK llio life 

 cycU", ill till' case of /'. ftijimoloi. Iiv foi'diiiif oxpi'riini'iitally 

 infoctod Cui'lops to thi" liotiiiilivo liost. Voiins iiialc ami finialc 

 worms won' found in tlu" liody cavity, from wluMici' tin' finialrs 

 siilisoiiut'iitly mittrati'd to their final liahitat in tlio tins. In 

 I'liilonu'tridao tlio motliod of ivscapo of the larvae is not as sp<> 

 eializod as in the ease of hrarunviiliis : the larvae of some spe 

 eies escape via the oviducts of the fish, while in the case of 

 I', fiijininloi the ripe viviparous females leave the fins of their 

 host, rupture, and liberate their larvae into the water. It is 

 easy to .see how the ffuine.-i worm life cycle could h;ivc evulvnl 

 from the camallanoid type liy the substitution of escape i)f 

 eiuliryos IhroUKh the skin for escape via the anus, which would 

 be very simple ia the case of parasites which reproduced in 

 parenteral habitats in acpiatic hosts. 



TRICHUROIDEA 



The membors of this superfamil.v, with the exccjition of 

 Trirhiiiilhi and CjixtDopxis (see below 1, have a simjile life cycle 

 eharactorizod by embryoiiation of eggn outside the body of the 

 host; access to a new host by swallowing of crks coutainiuK 

 first stage larvae provided with an oral spear; au<l direct mi 

 gration. via the blood stream if outside the alimentary canal, to 

 the site of developmi'nt. without jireliminary development el.se- 

 where in the body. The life cycle of CapiUaria col it m hii r , re- 

 cently worked out in detail by Wehr (IPH!)), will serve as an 

 example of the t.vpical Trichuroidea. 



C'APII.I..\RI.V COHMB.VF, 



The adults living in the small intestine are more or less im 

 bedded in the mucosa, but the eggs make their way into the 

 lumen and escape with the feces in an unsegniented state. 

 I'nder favorable conditions of temperature, moisture, and oxy- 

 gen segmentation occurs slowly, the first cleavage occurring in 

 about 48 hours, the morula stage in about .'•! days, and the in- 

 fective first-stage larva in t> to 8 days. No molting was ob- 

 served to occur in the egg. and hatching does not normally 

 take place before the egg is swallowed by a host. The entire 

 development from newly hatched larvae to adult worms takes 

 place in the small intestine of the definitive host. 



The first-stage larva, like all other trichuroid larvae, has an 

 oral spear. It has a long slender esophagus which posteriorly 

 lies superficial to and only partly imljcdded in the stichosome, 

 which consist of two rows of opposing cells. The intestine is 

 much shorter than the esophagus (ratio 1:3..")) and is termi- 

 nated by a short rectum. The anus is subterminal. 



The first molt occurs between 7 and 14 days after infection. 

 The second-stage larvae are slenderer, and appear to have no 

 oral spear; the stichosome consists of only a single row of cells, 

 and the intestine is relatively longer. The second molt occurs 

 about 14 days after infection. The third stage larvae are still 

 slenderer, with relatively longer intestine, and the genital iirim- 

 ordium is long. The third molt occurs between 14 and Til days 

 after infection. The fourth-stage larvae are very slender, and 

 sexually differentiated. The time of the final molt was not 

 determined, but some sexually mature adults with eggs were 

 found by the liHh day. 



Other TRicnrRiDAE 



The available evidence indicates that the life cycle of Tri- 

 chiirtK is essentially the same as that of CupiUaria ciilnmlxii , 

 and it is probalile that it is also the same for other species 

 of CapiUaria which inhabit the intestines of their hosts. The 

 aliility of CapiUaria larvae to use transport hosts was shown 

 by Wehr's (19.'!6 i demonstration that earthworms can serve as 

 vectors for C. annulata, the crop-worm of chickens. Fiilleborn's 

 (l!l23b) figures of Trichuris trichiura larvae are strikingly 

 similar to Wehr's figures of the first stage larva of CapiUaria. 

 .Mthough Neshi (IBIS, quoted by Yokogawa, l!l:20) reported the 

 finding of four larvae of Trichiiris vtilpix in the lungs of a dog 

 ■Jl hours after experimental infection, such migration on the 

 l>art of Trichuris has not been observed by other workers 

 either in normal or abnormal hosts (see Fiilleborn, ]!l23a). 



.As Vogel (li)30) pointed out, the entire group of Trichuroi- 

 dea show a remarkable tendency to localization during their 

 larval development in paiticular organs or tissues — what Vogcl 

 called "organotropism." In all cases except Trifliiiirlla this 

 organotropism continues throughout the adult life of the worms. 

 Different species of Trichuridae are known to develop and live 

 as adults in the esophagus, stomach, small intestine, cecum, 

 colon, respiratory tree, liver, spleen, urinary bladder, and 

 epithelium. The available evidence indicates that the newly 

 hatched larvae of those species which do not grow to maturit.v 

 in the intestine itself reach their destination by burrowing into 



the inlestiii.'il wall, entering the circulatory system, .'ind escap- 

 ing from the capillaries in the organ in which tlu'.v are to de 

 veloii (iood evidence for this li;is been obtained in the c'lsc of 

 CapiUaria iKpalira of the liver of rals. Vogel (lit.'iO) showe<l 

 that if young larvae of C. Inpat ira, recovered frinu the liver a 

 few <l;iys ;iftei' infection, were planted in the si)leen, lungs, or 

 under the skin, a few would succeed in reaching the liver. 

 Normall.v this worm penetrates the cecum, sometimes as early 

 as (i hours after infection (Lnttcrmoser, l!!38b), and is carried 

 directly to the liver via the hejjatic |)ortal system (Fiilleborn, 

 l'.>;;4; .Nishigori, lil:;.")), only an exceiitional few peru't rating 

 into the abdominal cavity, or being carried beycnid the liver 

 to the lungs :uid systemic cii'cnlation. In the cise of Tri- 

 (■liiisi>n\oi<l( s crassifaiula of the nr-in:u'y bt.-idder of i-ats, ^'oko- 

 gawa (UfJl) fed embryonatcd eggs to rats and 1 to 4 days 

 later fouini a few larvae in the abdominal and pleural cavities 

 and the lungs; these he thought were Trirlmsomoidrs larvae 

 from his fei'ding. but their size makes it evident that they 

 were not. 



.\n unusual situation with resjiect to transfer of infection to 

 new hosts exists in the case of CapiUaria hi'patica, which is sug- 

 gestive of a inissible step in the evolution of the TrichineUa life 

 cycle. The eggs of this worm are deposited in the liver tissues 

 of rats or mice, and reni;iiii there in an early stage of devel- 

 opment (one to four cells), viable for at least 7 or 8 months 

 (Luttermoser, l!t.'i8a). Only exceptionally do any of the eggs 

 escape from the liver to be voided with the feces, and eating of 

 an infected liver by a susceptible animal cannot result in infec- 

 tion because the nonembryonated eggs are not infective. 

 Momma (1!I30) suggested tlies as a factor in disseminating the 

 eggs from decaying carcasses, and also showed that eggs in 

 the feces of cats that have fed on infected rats .-ire viable. 

 Troisier and Di'schiens (19311) and Shorb (1931) independently 

 suggested that the usual method of transmission in n:ituie is 

 by ingestioii of eggs that have become embryonatcd after being 

 freed from the liver of an infected animal, either by decompo- 

 sition or by being eaten Ity another animal, usually the latter. 



Trichinell.\ spir.\i,is 



The life c.vcle of this worm is unique among parasitic nema- 

 todes in that the period of waiting for a new host is pas.sed in 

 the pniental host instead of in the open or in an intermediate 

 host. The life cycle of CapiUaria hepatica, described above, is 

 a ste|i in this direction, since in this case there are two periods 

 of waiting, one in the liver tissue of the parental ho.st, the 

 other (the usual one) after embryonation in the o])eu. In the 

 case of TrichineUa this double period is reduced to one by the 

 complete elimination of the usual period of waiting outside the 

 host, resulting from (1) precocious development to a burrow- 

 ing larval stage in the uterus of the mother, and (2) consequent 

 ability to infect the tissues of the parental host and to sub- 

 stitute development in this for the usual development in the 

 open or in an alternate host. 



The life cycle of this worm was one of the first to be worked 

 out in its essential features, contributions having been made by 

 Herbst, Kiicheumeister, Leuckart, and Virchow from 184S to 

 ISliO. The first entirely cojrect account of it was given by 

 Leuckart (IS(iO). The adult worms live in the small intestine. 

 The females produce no egg shells, and the ova, unlike those 

 of other Trichuroidea, develop precociously in the uterus, being 

 born as active burrowing larvae, though in a very early stage 

 of development, suggestive of microfilariae. There is an oral 

 spear as in other members of the group, but the alimentary 

 canal is rudimentary. This very immature larva enters the 

 circulation, passing capillaries in lioth liver and lungs, and is 

 distributed over the entire body. Presumably as the result of 

 a special organotropism as suggested by Vogel (1930), the 

 attraction in this particular case being the striated voluntary 

 muscles, the larvae leave the caiiillaries and immediately pene- 

 trate through the sarcolemma into the interior of muscle cells, 

 Iiossibly by means of extra-corporeal digestion. As to whether 

 the larvae actually penetrated into the muscle cells has long 

 been a matter of dispute, but seems finally to have been set- 

 tled by Jensen and Roth (1938). Immediately after penetra- 

 tion, accomplished b.v a boring movement of tlie spear-bearing 

 head end, the larva is seen lying lengthwise .iust under the 

 .sarcolemma, or between the sarcolemma and adjacent muscle 

 cells, .leusen and Koth think it likely that a histolytic enzyme 

 is also involved in the i)enetration of the muscle cells and in 

 dissolving the fibrillae inside. 



Once inside the cells the larvae come to rest and begin their 

 growth and differentiation, the muscle substance meanwhile 

 undergoing degenerative changes. By the 17th day, according 

 to .Jensen and Roth, the larva has grown from 100 to 400 or 

 .jOO m in length and has its esophagus and intestine clearly dif- 

 ferentiated. According to Stiiubli, however, it ma.v have in- 

 creased its length 10 times, to 800 to 1,000 M, in from 10 to 14 

 da.vs. After 11 days it begins to roll up spirally in a spindle- 



293 



