CJpn. J. Parasitol, Vol. 34, No. 2, 93-100, April, 1985]

Comments on Some Problems of of

Zai-bin KANG

(Received for publication ; May 17, 1982)

Key words: history,species, chromosome number, hybridization test, morphological characteri stics, integrative characteristics. Oncomelania

It is well-known that Oncomelania snails omelanian into three genera, eighteen species are the intermediate host of Schistosoma ja- and two subspecies on the basis of such stru ponicum, which is Asian pandemic. The ctures as shell, , radula, etc., pus geographical distribution of schistosomiasis hed the history of oncomelanian taxonomy cases entirely corresponds to that of Oncome into a period of enormous splitting. Later, lania snails. According to surveys made in Abbott recombined all oriental oncomelanians various endemic foci, wherever cases of sch (Continental parts as well as Taiwan Prov istosomiasis were found Oncomelania snails ince of China, Japan and Philippines) into were invariably present. But the taxonomy one , 4 species and one subspecies, and of those snails has been in a chaotic state thus brought about a period of enormous for a long time. In this paper, the writer merging. The result of all these revisions dwells on the following seven points. It is was that some investigators began to be ske hoped that the present work will serve as a ptical about the reliability of the basis of reference to further study on these snails. oncomelanian taxonomy ; some of them even 1. A confused historyof oncomelania ta went so far as to negate entirely the taxono- xonomy : It has been 103 years since the mical basis heretofore adopted, yet they did identification of Oncomelania hupensis by Gr- not offer a solution. The taxonomy of On edler in 1881, and in the literature there comelania has been subjected to frequent red- were 7 generic names (Oncomelania, Mela- ivision and recombination resulting in confu nia, Hemibia, Prososthenia, Blanfordia, Ka- sion. tayama and Schistosomophora) and 31 new 2. Oncomelanian taxonomy requires in- species (including subspecies). There is no depth investigation : While there was no co doubt that many of them were synonyms; mpatriot specializing in the classification of nevertheless, the possiblility still exists that Oncomelania, a considerable amount of work new species may remain undiscovered. Dur has been done in China on the embryological ing the past 103 years, there have been three development, morphology, anatomy and esp eminent oncomelanian taxonomists, namely, ecially on the ecology and eradication of Annandale (1924), Bartsch (1925, 1936a, Oncomelania; and in the meantime many 1936b, 1939, 1946), and Abbott (1948). An views on the taxonomy of Oncomelania have nandale was a pioneer in the thorough revi been proposed. The opinions of our scholars sion of oncomelanian taxonomy, combining are quite divergent, but one point in common the Chinese (including Taiwan) and the Jap is that they are aware of possible defects anese taxa into one genus (Oncomelania), and errors present in the work on oncomela two groups and five species in all ; and laid a nian taxonomy done abroad. The problem sound foundation for the taxonomy of this of oncomelanian taxonomy is still open, and snail. Bartsch, in dividing the oriental onc- awaits further investigation.

Department of Parasitology, Hubei Medical Co 3. Controversy of mono-species versus mu llege, Wuchang, China. lti-species : Despite the much diversified op-

( 53 ) 94 inions both at home and abroad on the tax to the same species. But whether this idea onomy of Oncomelania, by and large they is correct or not remains to be discussed. can be grouped into one of two schools. In recent more than ten years Davis (1967, One school maintains that Oncomelania of 1968, 1969 a, 1969 b, 1971, 1973) has studied the world consists of more than one species, the oncomelaniid snails of Taiwan, Japan, whereas the other school suggests that Onc Philippines and Indonesia. His work is very omelania consists of one genus and one sin careful and his papers are well worth read gle species only. The argument for the for ing, but his idea of Oncomelania taxonomy mer school is that Oncomelania of the world is not necessarily correct. His idea funda has conspicuous morphological distinctions; mentally but not entirely agree with Burch's they are also different with respect to geog (1966, 1967). Davis recognizes only one gen raphic distribution, ecology, physiology, ont us with two species and six subspecies. Th ogeny, immunology and infectivity ; therefore ese taxa are Oncomelania minima from Japan more than one species is present. Most of and the subspecies of Oncomelania hupensis, the oncomelanian research workers in this i.e., O. h. hupensis from mainland China; country and abroad adhere to this view (He- O. h. chiui and O. h. formosana from Tai ude, 1890; Annandale, 1924; Bartsch, 1925, wan ; O. h. nosophora from Japan ; O. h. 1936 a, 1936 b, 1939, 1946; Germain et Ne- quadrasi from the Philippines ; O. h. lindo- veu-Lemaire, 1926; Baylis, 1931 ; Bequaert, ensis from Sulawesi in Indonesia. It is quite 1928, 1934; Abbott, 1948; Yasuraok, 1969, clear that Davis incorporated all the Chinese 1970 ; Sun, 1964), and the writer also shares oncomelaniid snails into a subspecies Onco- their opinion (Kang et al., 1958; Kang, tmelania hupensis hupensis. We considered 1981). Concerning the oncomelanian taxono it is very incorrect. As is known to all, my we will deal with in another article in mainland China is the most important distr detail. We consider that Oncomelania hup- ibuting centre of Oncomelania, where the ensis, O. formosana, O. nosophora, O. qua- vector snail of Schistosoma japonicum is wi- drasi, O. chiui, O. minima, O. tangi, and despred in 12 provinces and 347 counties. O. robertsoni are all distinct species rather Its natural conditions are very complex, and than the same species. species may be numerous. Regrettably, Da The idea of only one genus and one species vis has not studied the Chinese oncomelaniid is held by Kuo and Mao (1957) who proposed snails. Thus his work of Oncomelania tax that the specific term Oncomelania hupensis onomy should not be considered complete. Gredler should be used for all Oncomelania Liu, Y. Y. (1974) first considered that all snails involved in the transmission of sch- the Chinese oncomelaniid snails are probably istosomiasis japonica in China. But later of only one species {Oncomelania hupensis) Mao et al. (1965) also said : "the views with a number of subspecies, but afterwards of our scholars are still divergent on the tax Liu et al. (1981) said all the oncomelaniid onomy of the genus Oncomelania, in line snails distributed throughout the world sho with the materials now available it could uld be regarded as a single species, and not come to a conclusion, and waits for classified it into 10 subspecies. These subs researches." pecies all were originally distinct species. Burch (1960 b, 1964, 1966, 1967) found that They reduced these species to subspecies and the four species (O. hupensis, O. formosana, changed their scientific names from binomial O. quadrasi and O. nosophora) all have the nomenclature into trinomial nomenclature. same number of chromosomes: n = 17, 2n = We considered their justification for doing 34. This cytological finding, coupled with this is not entirely warranted. This change the readiness of hybridization as well as the could only create taxonomic confusion. hybrids' capability of producing fertile offs 4. The criterion of chromosome number pring, led Burch to refer these four species is not yet up to the level of species identi-

( 54 ) 95 fication : Burch's view may seem justified belonging to the same species, then all the at first glance, but may not be correct. In species of the genus Bulinus and the genus order to elucidate the problem, a considera Biomphalaria should be merged into one tion on the usefulness of chromosome number species. Yet Burch did not say that they are for taxonomical work seems necessary. Acc of the same species; on the contrary he ording to the literature available to us, chro admitted that chromosome numbers, as a ge mosome number is of limited significance neral chracteristic, could not facilitate the in taxonomical work. It cannot serve as the taxonomy of these snails. sole criterion for the classification of mollus- Recently I received a letter from Professor can species. Likewise, it cannot serve as the Tan Jia-zhen, the Chinese geneticist, in wh sole criterion of oncomelanian taxonomy. ich he pointed out : "(1) The number of Early in 1960, Burch himself pointed out chromosomes is not a definite indicator of that the monocentric and elongate features species because different species may have of chromosomes are the same with aquatic the same number of chromosomes. For exa pulmonate snails as with terrestrial ones, and mple Triticum dicoccum and Triticum dico- cannot be used to distinguish the two Order ccoides are different species, but their mor (Basommatophora and Stylommatophora). phology and number of chromosomes are Eight species belonging to five families of the same. (2) The individuals of the species Basommatophora have no pronounced differ may have different number and morphology ence in the configuration of chromosomes. of chromosomes such as the individuals of As to the number of chromosomes, the hap- Catantops brachycerus Will, have different loid number are all 18 except one species chromosome morphology. Such instances are (n = 17); thus, he admitted that chromosome too numerous to mention." Therefore, based number by itself has very limited value. on the data available, chromosome number Patterson (1967), on the basis of published in snails cannot serve as the basis of species literature, tabulated the chromosome numb identification. The identical chromosome ers of streptoneuran snails, most of the species number in the four species of Oncomelania having the same number of chromosomes. can only indicate that they are of the same If species with the same chromosome number genus, but not the same species. should be reckoned as of the same species, 5. The significance of hybridization test then the numerous species in Streptoneura in oncomelanian taxonomy : The value of would be "merged" into one and the same the hybridization test to oncomelanian tax species. onomy also needs discussion. Wagner et al. We find that Burch's view (1966, 1967) (1957, 1959), Komiya et al. (1958, 1959, 1960) on the taxonomical significane of chromosome and Davis et al. (1965) succeeded in the hy number with reference to the intermediate bridization of oncomelanian species and obta host of human schistosomiasis have been inc ined fertile offspring. On this ground, Ko onsistent and contradictory. He considered miya et al. raised the question of whether the four species of Oncomelania to be the O. nosophora and O. hupensis are really same species on the grounds that they all two distinct species. Wagner et al., on the have 17 pairs of chromosomes. But, in his other hand, pointed out that if experimental study on 23 species of Bulinus, the interme hybridization can serve as the criterion of diate host of Schistosoma haematobium, 15 species identification, then the four oncome species have the haploid number of 18. His lanian taxa should be regarded as four sub observation on 5 species and 2 subspecies of species, yet for the convenience of clinicians Biomphalaria, the intermediate host of S. and public health workers, they should retain mansoni, disclosed that they all have 18 pairs their original scientific names so as to avoid of chromosomes. If species with the same confusion. chromosome numbers should be regarded as Sun Zhen-zhong (1964), having analysed

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Wagner's results of hybridization, pointed Oncomelania possesses varying degree of sus out: "The external morphological features ceptibility to infection with geographic str of some of the offspring resembled the pate ains of Schistosoma japonicum (Hunter et rnal parent, some resembled the maternal al., 1952; DeWitt, 1954 : Pesigan et al., parent, yet the paternal and maternal par 1958; Vogel, 1948; Yuan, 1958; Hsu et al., ents were of two taxa. Morphological feat 1960; Moose et al., 1963 b; Chiu, 1967). ures of both taxa can pass to the Fi hybrids In recent years the susceptibility of Oncome through heredity. In other words, whereas lania hybrid snails to schistosome infection either taxon has inheritable characteristics of has been reported. According to the report its own, both features can pass to the Fi of Moose and Williams (1963 a), trie Japan generation ; since each taxon possesses inhe ese strain of S. japonicum did not develop ritable capacity, it fulfills the characteristics in the hybrid of O. nosophora and O. formo of a species. Therefore, the four taxa used sana. Chi et al. (1971) pointed out that in the hybridization test were not of the the infection rate in hybrid snails (7.1%) is same species. Besides, the copulation rate, lower than that in the geographically natural fecundity and duration of breeding season snail hosts (22.4%). Chiu et al. (1981) obse are higher and more condensed in the cro rved that Oncomelania recombinants or hyb ssings within the same taxon than in the rids were found to be susceptible to the orig crossings between different taxa, and this is inal strain of S. japonicum, however, the an evidence of the four taxa used in hybrid susceptibility declined markedly by each ge ization tests being not of same species." neration. This difference in susceptibility al Hsu and Hsu (1960) believed that the four so indicated that these taxa of Oncomelania species mentioned above, of Oncomelania were not of the same species, though hybrid became distinct not only physiological but ization between them did occur. also morphologically, therefore, they are four Besides, van der Schalie, Getz and Dazo distinct geographical species rather than the (1962) reported the success of crossing between same species. But because isolation is not these species (Oncomelania formosana, O. complete, interspecies breedings are still quadrasi) and the American possible. lapidaris. In his book ^Historical Laws of Davis et at. (1965) crossed a female O. Biological Development^ Chen Shi-xiang quadrasi with a male O. formosana and (1978b) wrote: "At Gaogang Commune of obtained one single male hybrid, which was Fenyi County in Jiangxi Province, cattle was abnormal in many aspects. Externally, the put out to pasture together with water buffalo antennae had many branches, and there were over a long period of time. Eventually the 7 eye masses. Internally, the salivary glands hybridization between them has met with were malformed, the antennal nerve became success and the hybrid produced has been greatly thickened, the sex glands showed propagating many generation." These facts atrophy. This abnormal male hybrid was demonstrate even more clearly that intersp reared together with several normal female ecific hybridization, intraspecific hybridization, hybrids in the laboratory for 21 months, but as well as distant species hybridization, is no offspring was produced although copulat possible. Therefore, the four species ment ion took place often. This fact indicates ioned above, of Oncomelania (O. hupensis, that O. quadrasi and O. formosana are not O. formosana, O. nosophora, O. quadrasi) of the same species. Yet Davis et al. held are not of the same species, though they that thousands of hybrids were normal, the could hybridize artificially. vitality of Fi and F2 was not weakened ; Taxonomists of the past deemed infertile indicating that these Oncomelania were of hybridization as the classical criterion of sp subspecific or conspecific nature. ecies : taxa that produce fertile hybrids are It is well known that different species of considered to be the same species, those pro-

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ducing infertile hybrids are considered as 7. Integrative characteristics should be ad different species. In general, this idea is opted in subsequent taxonomical study of On still in vogue as a criterion of species at comelania : The 103-year history of taxono present, but, just as Chen Shi-xiang (1978 a) mical study on Oncomelania demonstrates th indicated, the application of this criterion at none of the single characteristics is satis has certain limits, and the demarcation line factory. Morphological characteristics are of infertile hybridization is also not absolute. more convenient and practical but sometimes Under given condition, different species and it is not sufficient to rely on morphological even distant species can also hybridize and features alone, especially in cases of closely produce a generation of fertile hybrids. allied species, for which an identification ba 6. Morphological characteristics are imp sed solely on morphology would be extremely ortant in taxonomy : All classification of an difficult. As to chromosome number, the li imals used morphological structures as the terature has documented that most of the chief characteristic for the convenience not snails have the same number ; thus chromo only of recognizing the species, but also of some number does not afford sufficient criteria practical application. The morphological for species identification. Hybridization tests characteristics of each species have in general are fairly important for taxonomical been formed through long stages of evolution study, but their application has met with in a given environment and thus imply much certain limitations ; there are cases of inte importance. Although morphological varia rspecific hybrids formed as a result of inco tion may occur under the influence of envir mplete isolation, thus making a discrimina onmental factors, in most cases morphological tion of species difficult. From what appears characteristics of , once formed, can in the current literature, hybridization tests pass on generation after generation. Generally also cannot be used as the sole criterion of speaking, morphological difference reflects oncomelanian taxonomy. What should be indirectly the genetical difference, thus mor taken as the basis of classification then? We phological characteristics may be taken as suggest the adoptation of integrative characte the basis of classification. Chen Shi-xiang ristics. The more data of characteristics av (1964) wrote : "Morphological characteristics ailable, the more scientific the taxonomic as a basis of classification reflect the study will be. Specifically, we mean to take unification between continuity and inte morphological characteristics as the basis, wh rruption through the unification of the morph ich, in conjunction with ecological, physiolo ological conformity and specificity. That is gical, biochemical, ontogenetic, cytogenetical to say, phylogenetical homogeneity and con and zoogeographical characteristics, allow in tinuity are reflected by morphological con tegrative and comparative study, so as to formity, whilst divergence and interruptions elucidate the species composition of Oncome are reflected by morphological specificity. lania and its phylogenetic relationship. This Therefore, morphological characteristics have would not only be of theoretical interest, the significance of "marking in a twofold but also important in practice, for prophyla sense : as a mark of classification and as a xis and therapy of schistosomiasis caused by mark of phylogeny. These two markings Schistosoma japonicum. must be unified." Heude (1890), Annandale Summary (1924), Bartsch (1925, 1936 a, 1936 b, 1939, 1946) and Abbott (1948) all based their classi The present paper deals with seven tax fication on the morphology of Oncomelania. onomic problems in the molluscan genus On Despite of shortcoming and errors in their comelania. During the 103-year history it taxonomical studies, we should in no way may be found that the taxonomy of Oncom negate the importance of morphological attr elania has been subjected to redivision and ibutes to taxonomical study. recombination once and again and has fallen

( 57 ) 98 into utter confusion. But the problem of molluscan hosts of the Schistosomes parasitic Oncomelania taxonomy has not yet been reso- in man. Ann. Trop. Med. Parasitol., 25, Ived and still awaits for deep-going researches. 369-372. The value of the chromosome number, hybridiz 9) Bequaert, J. (1928): Mollusks of importa ation test and morphological characteristics on nce in human and veterinary medicine. Am er. J. Trop. Med., 8, 165-182, 215-232. the taxonomy has been discussed. A temporal 10) Bequaert, J. (1934) : The molluscan interm conclusion may be made that the chromosome ediate host of the blood fluke, Schistosoma number can not be used as a taxonomy mark japonicum Katsurada, in the Philippines. on the level of species yet, nor is hybridiza With a note on the genus Blanfordia by tion test as the sole criterion of oncomelanian H. A. Pilsbry. J. Parasitol., 20, 280-284. taxonomy. So the morphological character 11) Burch, J. B. (1960 a): Chromosome morp istics are still an important and valuable hology of aquatic pulmonate snails (Mollus- parameter in taxonomy. The author does ca : Pulmonatd). Transa. Amer. Micro. So- not agree with Liu et al. (1981) that there is ci., 79, 451-461. only one genus and one species of Oncome 12) Burch, J. B. (1960 b): Chromosomes of Po- matiopsis and Oncomelania. Amer. Malacol. lania all over the world. Many evidences Union Ann. Reps., 26, 15-16. are presented to favor the view that it consists 13) Burch, J. B. (1964) : Cytotaxonomy of the of more than one species. A suggestion has genus Oncomelania, intermediate hosts of been made that the integrative characteristics Schistosoma japonicum. Amer. Malacol. Un should be adopted in subsequent taxonomical ion Ann. Reps., 31, 28-29. study of Oncomelania. 14) Burch, J. B. (1966): Chromosomes of in termediate hosts of human bilharziasis. Ma- References lacologia, 5, 25-27. 1) Abbott, R. T. (1948) : Handbook of medi 15) Burch, J. B. (1967) : Chromosomes of in cally important mollusks of the Orient and termediate hosts of human bilharziasis. Ma- the Western pacific. Bull. Mus. Comp. Zool., lacologia, 5, 127-135. Harvard Coll., 100, 245-328. 16) Chen, S. X. (1964): Taxonomic principles 2) Annandale, N. (1924) : The molluscan hosts of morphological characteristics. KEXUE of the human blood fluke in China and TONGBAO, 9, 770-779 (in Chinese). Japan, and species liable to be confused 17) Chen, S. X. (1978 a) : Evolution and Tax with them. Amer. J. Hyg. Monogr. Ser. 3, onomy. 51pp. Science Press, Beijing (in 269-294. Chinese) 3) Bartsch, P. (1925) : Some new intermediate 18) Chen, S. X. (1978 b): Historical Laws of host of the Asiatic human blood fluke. J. Biological Development. 130 pp. Science Pr Washington Acad. Sci., 15, 71-73. ess, Beijing (in Chinese). 4) Bartsch, P. (1936 a) : Molluscan intermedi 19) Chi, L. W., E. D. Wagner, and Nancy ate hosts of the Asiatic blood fluke, Schisto Wold (1971) : Susceptibility of Oncomelania soma japonicum, and species confused with hybrid snails to various geographic strains them. Smithsonian Misc. Coll., 95, 1-60. of Schistosoma japonicum. Amer. J. Trop. 5) Bartsch, P. (1936 b): A new intermediate Med. & Hyg., 20, 89-94. host of the Asiatic blood fluke, Schistosoma 20) Chiu, J. K. (1967): Susceptibility of Onc japonicum {Katayama tangi). Proc. Biol. omelania hupensis chiui to infection with Soc. Washington, 49, 139-142. Schistosoma japonicum. Malacologia, 6, 145 6) Bartsch, P. (1939) : A new intermediate ho -153. st of the Asiatic blood fluke, Schistosoma 21) Chiu, J. K., S. J. Ong, J. C. Yu, C. Y. Kao japonicum Katsurada. {Oncomelania yaoi). and T. Iijima (1981) : Susceptibility of Onco J. Washington Acad. Sci., 29, 173-174. melania hupensis formosana recombinants 7) Bartsch, P. (1946): Schistosomophora in and hybrids with Oncomelania hupensis noso- China, with descriptions of two new species phora to infection with Schistosoma japon and a note on their Philippine relative. Sm icum. Int. J. Parasitol., 11, 391-397. ithsonian Misc. Coll., 104, 1-7. 22) Davis, G. M., J. W. Moose, and J. E. Wi S) Baylis, H. A. (1931): The names of some lliams (1965): Abnormal development in

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a hybrid Oncomelania (: Hy- Oncomelania formosana. J. Parasitol., 38, drobiidae). Malacologia, 2, 209-217. 492. 23) Davis, G. M. (1967) : The systematic rela 35) Kang, T. P., Wang, T. K., and Chou, S. tionship of Pomatiopsis Lapidaria and Onco L. (1958) : Studies on the geographical dis melania hupensis formosana {Gastropoda : tribution and morphology of the Oncome- Hydrobiidae). Malacologia, 6, 1-143. laniid snails, an intermediate host of Schist 24) Davis, G. M. (1968) : A systematic study of osoma japonicum in Hupeh Province, China. Oncomelania hupensis chiui (Gastropoda: Acta Zoologica Sinica, 10, 225-241 (in Ch Hydrobiidae). Malacologia, 7, 17-70. inese). 25) Davis, G. M. (1969 a): Reproductive, neu 36) Kang, Z. B. ( = Kang, T. P.) (1981): Mor ral and other anatomical aspects of Oncome phology and distribution of Oncomelania lania minima (Prosobranchia : Hydrobiid (Katayamae) tangi (Bartsch, 1936) in Fujian ae). Venus, Jap. J. Malacology, 28, 1-36. Province, China. Acta Hydrobiologica Sini 26) Davis, G. M. (1969b): Oncomelania and ca, 7, 313-325, pis. MI. (in Chinese). the transmission of Schistosoma japonicum : 37) Komiya, Y., and Kojima, K. (1958): A A brief review, in : Harinasuta, C. (ed) crossing experiment of Oncomelania noso Proc. 4 th Southeast Asian Sem. Parasit. phora with O. hupensis. Preliminary report. Trop. Med., Schistosomiasis and Other Sn Jap. J. Med. Sci. Biol., 11, 185-186. ail-Transmitted Helminthiasis, p. 93-103, 38) Komiya, Y., and Kojima, K. (1959): The Bangkok. production of F? offspring from Ft (hybrids) 27) Davis, G. M. (1971) : Mass cultivation of of Oncomelania nosophora and O. hupensis. Oncomelania {Prosobranchia : Hydrobii J. Parasitol., 45, (Section II), 23-24. dae) for studies of Schistosoma japonicum. 39) Komiya, Y., K. Kojima, and T. Koyama In "Culturing Biomphalaria and Oncomela (1960) : The production of F2 offspring nia (Gastropoda) for Large-Scale Studies of from Fi (hibrids) of Oncomelania nosophora Schistosomiasis. "Bio-Medical Reports of the and O. hupensis. Jpn. J. Parasitol., 9, 22 406 Medical Laboratory, No. 19, 85-161. (in Japanese). 28) Davis, G. M., and W. P. Carney (1973): 40) Kuo, Y. H., and Mao, S. P. (1957): On Description of Oncomelania hupensis lindo- the taxonomy of Oncomelania Snail host ensis, first intermediate host of Schistosoma of Schistosoma japonicum. Morphological japonicum in Sulawesi. Proc. Acad. Nat. studies of Oncomelania snails from different Sci. Philadelphia, 125, 1-34. endemic areas in China. Chinese Med. J., 29) DeWitt, W. B. (1954): Susceptibility of sn 75, 824-831. ail vectors to geographic strain of Schisto 41) Liu, Y. Y. (1974) : Notes on the classifica soma japonicum. J. Parasitol., 40, 453-456. tion of the Chinese oncomelaniid snails. 30) Germain, L., and Neveu-Lemaire (1926): Acta Zoologica Sinica, 20, 223-230 (in Ch Study on medical Malacology. Ann. Para inese). sit., 4, 286-307, 352-384. 42) Liu, Y. Y., Lou, T. K., Wang, Y. X., 31) Gredler, V. (1881): Zur Conchylien-Fauna and Zhang, W. Z. (1981): Subspecific diff von China. Jahrb. Deutsch. Malakoz. Ges., erentiation of oncomelaniid snails. Acta Zoo- 8, 110-132. taxonomica Sinica, 6, 253-267 (in Chinese). 32) Heude, P. M. (1890): Notes sur les moll- 43) Mao, S. P. et al. (1965): Studies on the usques terrestres de la Vallee Fleuve Bleu. eradications of Oncomelania. 132 pp. Scien Mem. Concern. Hist. Nat. Emp. Chinois, ce and Technology Press, Shanghai (in Ch 125-188, pis. 33-43. inese). 33) Hsu, S. Y. Li, and Hsu, H. F. (1960): 44) Moose, J. W., and J. E. Williams (1963a): Infectivity of the Philippine strain of Schist Infectivity of hybrid snails obtained from osoma japonicum in Oncomelania hupensis, the reciprocal cross of Oncomelania nosop O. formosana and O. nosophora. J. Para hora and O. formosana to the Japanese sitol., 46, 793-796. strain of Schistosoma japonicum. J. Para 34) Hunter, G. W. Ill, Ritchie, L. S., and sitol., 49, 284. Otori, Y. (1952) : A comparison of the inf 45) Moose, J. W., and J. E. Williams (1963b): ectivity of Schistosoma japonicum occurring Susceptibility of Oncomelania formosana fr in Japan for Oncomelania nosophora and om three different areas of Taiwan to infe-

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ction with Formosan Strain of Schistosoma (1957): Species crossing in Oncomelania. japonicum. J. ParasitoL, 49, 702-703. Amer. J. Trop. Med. Hyg., 6, 376. 46) Patterson, C. M. (1967): Chromosome nu 52) Wagner, E. D., and W. L. Chi (1959): mber and systematics in streptoneuran snails. Species crossing in Oncomelania. Amer. J. Malacologia, 5, 111-125. Trop. Med. Hyg., 8, 195-198. 47) Pesigan, T. P., Hairston, N. G., Jauregui, 53) Yasuraoka, K. (1969) : Snail vectors in sch- J. J., Garcia, E. G., Santos, A. T., Santos, istosomiasis japonica. in: Harinasuta, C. B. C, and Besa, A. A. (1958): Studies on (ed) Proc. 4 th Southeast Asian Sem. Para- Schistosoma japonicum infection in the Phi sit. Trop. Med., Schistosomiasis and Other lippines. 2. The molluscan host. Bull. W, H. Snail-Transmitted Helminthiasis, p. 83-88, O., 18, 481-578. Bangkok. 48) Sun, Z. Z. (1964) : Recent advances in res 54) Yasuraoka, K. (1970): Some recent resea earches on medical Conchology. JIANGXI rch on the biology and control of Oncome YIYAO 4, 233-235, 222 (in Chinese). lania snails in Japan. Recent advances in 49) Van der Schalie, H., Getz, L. L., Dazo, researches on filariasis and schistosomiasis B. C. (1962): Hybrids between American in Japan edited by Manabu Sasa, 291-303. Pomatiopsis and Oriental Oncomelania sna University of Tokyo Press. ils. Amer. J. Trop. Med. Hyg., 11, 418- 55) Yuan, H. C. (1958): A preliminary study 420. on the susceptibility of geographic strains 50) Vogel, H. (1948) : Uber eine dausrzucht von of Oncomelania hupensis to geographic str Oncomelania hupensis and infektionsversuche ains of Schistosoma japonicum from 6 diffe mit Bilharzia japonica. Ztschr. ParasitoL, rent provinces in China. Chinese Med. J., 14, 70-91. 77, 575. 51) Wagner, E. D., D. Inaba, and L. W. Wong

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