1.The bionomics of Oncomelania snails in Soochow (Kiangsu Province), Kashing, Hangchow, Chuhsien and Kaihua (Chekiang Province) were studied from October 3 to November 19, 1948. The results were described separately for different localities. The species of snails were assumed, according to the studies of former investigators, to be O. hupensis in Soochow, Kashing and Hangchow and O. nosophora in Chuhsien and Kaihua.
2.In the Soochow area, O. hupensis was found most frequent in the irrigation ditches, and nex in frequency in the terminal canals. They were sometimes present in certain portions of the tertiary or secondary canals. Even in the primary canals they were occasionally found along certain stretches of the banks. They were sometimes present in the rice fields, but were usually confined only to the immediate vicinity of the fields which were near the inlet of the irrigation ditches. However, they were absent in the ponds. The distribution of the Oncomelania was especially conditioned by the amount of humus, moisture, shade and vegetation in or on the soil of the banks of the ditches or canals.
3.That Oncomelania could climb a tree, Evonymus bungeana, up to 2.25 meters from the bank of a tertiary canal, was found at Mao Chia Wu, Hsü Kou, Soochow and this fact is herein reported for the first time.
4.In the Kashing area, the habitat of Oncomelania hupensis was found in locations similar to those described for the Soochow area. Their presence or absence was determined mainly by the character of the soil on the banks rather than by the size of the canal.
5.In the Hangchow area, Oncomelania hupensis was found both in the canals and the irrigation ditches. The determining factors for their presence or absence depend on the character of the soil together with other environmental conditions mentioned above.
6.In the Chuhsien area, Oncomelania nosophora was found mainly in the irrigation ditches and also, although less often and not as numerous, in the rice fields.
7.In Kaihua, the habitat of O. nosophora was found in locations similar to those in Chuhsien. The finding of this species on the banks of certain portions of mountain brooklets is a new observation.
8.The results of my studies in the five places mentioned above indicate that the habitats of O. hupensis and O. nosophora were similar in certain details. Both species were easily found in the irrigation ditches and under the same conditions with regard to the presence of humus, moisture, shade and vegetation in or on the soil of the banks of a ditch or a canal. Their habits differ in that O. nosophora was more easily found in the rice fields than O. hupensis, and also that O. nosophora could be found on the banks of certain mountain brooks where O. hupensis has not hitherto been reported.
9.Pairing of Oncomelania snails was observed from October 3 to November 19 for both O. hupensis and O. nosophora in all five localities. Some young snails were also seen during this period in these five places. One important fact noted was that young snails were more easily found in the irrigation ditches than in the canals, and in one instance on October 5, numerous young snails of O. hupensis were found in one particular ditch at Hsi Ku Tsun, Hsü Kou, Soochow.
10.An all-year-round observation on the pairing and the emergence of young snails of Oncomelania snails in various places is suggested.
Department of Zoology, National Taiwan University, Taipeh, Formosa.