1. Thirty-three discinid larvae were obtained one meter below the water surface in the daytime in the shallow part of the Johore Strait, north of Singapore. 2. The oldest among them, 462 µ in longitudinal diameter, resembled the "Mueller's larva" discovered by Mueller and referred to Pelagodiscus atlanticus (King) by many subsequent authors. 3. The youngest among them, 108 µ long and 115 µ wide in dorsal shell, resembled Simroth's smaller discinid larva of 220 µ diameter in many essential features. 4. The larvae in this study showed a gradual transition in many morphological characters, indicating that they were a series of developmental stages in the ontogeny of a single discinid species. 5. The two bunches of long embryonic setae were gradually replaced by the curved early larval setae in the medium-sized specimens. Towards the close of the larval stage the third kind of setae appeared from the mantle border. 6. The dorsal shell valve maintained its oval shape during the entire larval stage. The posterior edge of the ventral one, however, gradually changed from convex to concave, passing through a stage when it was almost a straight line. 7. The statocysts and the pedicle appeared in older larvae. 8. The number of cirri remained constant throughout the larval stage. 9. The larvae were compared with the discinid larvae previously recorded. Their developmental changes and the breeding season of discinids were discussed.
1. Study of the structure and mode of life of Malleus regula provides the basis for consideration of the "hammer" species, M. malleus and M. albus. 2. M. regula occurs byssally attached, vertically disposed on rocky substrates associated with mud and is widely distributed in the tropical Indo-Pacific. 3. The distal two-thirds of the elongated shell is exclusively prismatic. By means of special pallial retractors the mantle lobes can be withdrawn within the nacreous region. 4. The massive opisthodetic ligament has a short secondary extension of fusion layer. 5. A promyal chamber on the right side proximal to the adductor increases water flow into the exhalant chamber. 6. The long filibranch ctenidia provide a vertically extended food-collecting surface. 7. The foot is concerned with planting of the massive byssus which emerges through a notch in the right valve but on the under ( i.e., dorsal) surface. There is also a unique and very long accessory foot, ventrally grooved, everywhere ciliated and in constant writhing activity due to blood pressure and intrinsic muscle. Moving freely throughout the lower mantle cavity it can only be concerned with cleansing. 8. Pseudofaeces are ejected from the distal tip of the mantle cavity. 9. M. malleus, the black hammer shell, occurs vertically embedded in coarse sand or sandy gravel. Byssus threads are attached to fragments within the substrate. The great anterior and posterior elongations of the hinge line (also exclusively prismatic) are separated by the byssal notch (now affecting both valves). 10. Shells are usually excessively irregular due to the great exposure to damage and the almost unlimited powers of rapid repair by the three pallial extensions. 11. M. albus, the white hammer shell, is stouter and inhabits muddy sand. During growth it loses the byssus with reduction of the foot and byssal retractors and closure of the byssal notch. The accessory foot is not affected. The animal becomes anchored in the substrate exclusively by the anterior and posterior extensions of the shell. 12. Description of the typically rounded Isognomon ephippium leads to that of the elongated I. isognomon which occupies precisely the same habitat as M. regula. 13. It lacks the pallial retractors, promyal chamber and accessory foot of Malleus, the nacreous region is more extended distally and the ligament is multivincular (the formation of which is discussed), producing some posterior, but never any anterior, extension of the hinge line. 14. A remarkably dense mixed bed of M. regula and I. isognomon in Darvel Bay, Sabah (Borneo), is described. Different spawning periods, by preventing competition during settlement, may account for this complete intermixing of sympatric species, which, however, are generalized herbivores where numbers are not limited by food supply. 15. From a basic epifaunal habit (Pteria, Isognomon, M. regula), members of the Pteriacea have become adapted for infaunal life within sponges (Vulsella, Crenatula) or within soft substrates ( M. malleus, M. alba and the Pinnidae). 16. There is final discussion about elongation in monomyarians, i.e., in the genus Malleus and in I. isognomon.
The fluorescent antibody (FA) technique was used to detect the presence of malarial antibody in populations living in 3 different ecological areas of Malaysia. Serum samples were tested using Plasmodium falciparum, P. vivax, P. malariae and P. fieldi antigens. An area of hyperendemic malaria had a good correlation between the antibody responses and active parasitaemias. The percentage and intensity of responses increased with the age of the individuals. In an area of hypoendemic malaria, each of 17 sites had ecological conditions which would favour or discourage the transmission of malaria. The reasons for high FA responses in some villages and low responses in others were readily apparent. The effect of even limited control programmes on the malarial ecology could be measured by an examination of the antibody responses. An aboriginal population receiving suppressive drugs had FA responses indicating both past experience and the effect of the drug programme.
In certain areas of Sabah, East Malaysia, local houses are frequently built without walls or with incomplete walls. Also, the people in these areas often refuse permission for their houses to be sprayed inside with insecticide (DDT). These special conditions are the reason for the persistence of malaria transmission under a WHO malaria eradication programme.Field trials were conducted in specially constructed huts, similar to the local houses, in which all-night collections of mosquitos were made, both those biting human baits and those resting on walls, in order to determine (1) the effectiveness of spraying DDT in houses without, or with incomplete, walls; and (2) the best way to protect people against mosquito bites with DDT-spraying where the house-owners have refused indoor spraying.The results indicate that (1) as expected, DDT-spraying inside a hut with incomplete walls is less effective than in a hut with complete walls, especially 6 months or more after spraying; (2) external spraying of walls with DDT at double the normal dose (i.e., 4 g/m(2)) greatly reduced contacts between man and mosquito and thereby limited transmission of malaria.
The immunological characteristics of 26 strains of Japanese encephalitis virus (JEV) isolated in Japan and Malaya between 1935 and 1966 have been investigated mainly by the antibody-absorption variant of the haemagglutination-inhibition test, and to a certain extent also by conventional haemagglutination-inhibition and complement-fixation tests. The antibody-absorption technique shows promise as a routine method for the immunotyping of JEV.At present, two immunotypes can be distinguished. One comprises 2 strains, Nakayama-NIH and I-58, and is designated as the I-58 immunotype. The other immunotype, JaGAr 01, comprises 17 strains which share the characteristics of the JaGAr 01 strain, including one subline of the Nakayama strain, Nakayama-Yakken. The Nakayama-RFVL strain was found to have the characteristics of both immunotypes. The I-58 immunotype differs more markedly from related arboviruses, such as the Murray Valley encephalitis virus and the West Nile Eg101 strain, than does the JaGAr 01 immunotype.Evidence is presented which suggests that a given JEV strain can change immunotype on repeated passage through mice.