A study has been made on the intestinal pathology of the marine fish, Rachycentron canadus parasitised by the acanthocephalid worm, Serrasentis nadakali. Evidence indicates that the worm infection causes hyperplastic, metaplastic and hypertrophic changes involving respectively connective tissue, epithelial and muscle cells of the fish intestine. The worm attachment to the intestinal wall causes destruction of the villi, degeneration and necrosis of the mucosal epithelium. Cell types resembling epitheloids, lymphocytes, macrophages and cells of unknown identity aggregate at the infected area in response to inflammation. Excessive mucus secretion has also been observed.

In vivo development of Echinostoma malayanum Leiper, 1911 was studied in white rats and the developmental process was arbitrarily divided into four stages: organogeny, vitellogenesis, formation of Mehlis' gland complex and cirrus sac, and oviposition. The percentage of development was 86-94. Population density affected the prepatent period of flukes and the normal prepatent period of 13-16 days was altered to 18-23 days in infection with 500-800 flukes. The majority of flukes in heavy infection were undersized and in the immature stage of development at patency. Data from chemical analysis of flukes revealed that protein, lipids, calcium and ash decreased quantitatively in flukes from higher population densities but no such change was observed as regards glycogen. Pathological changes in the rat intestine included lysis and destruction of mucosa, increased activity of goblet cells, oedematous and reticulated appearance of lamina propria and slight to moderate hyperplasia of epithelial cells. The metacercariae excysted in the medium containing trypsin plus sodium cholate an pepsin, though not essential for a high percentage of excystment, affected the rate. The reductant sodium dithionite substantially enhanced the rate and percentage of excystment. Excystation was optimal at pH 8, and 42 degrees C was more effective than 39 degrees C.

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The life cycle of Pallisentis nagpurensis involves the fish Ophiocephalus striatus as the final host and the copepod Cyclops strennus as the intermediate host. The embryonated eggs are adapted to float in water. The development of the acanthors up to the stage of infective acanthellae takes place in the haemocoel of the cyclops in 15-20 days. The juveniles develop to maturity in the intestine of the fish after about 50 days. Incompletely developed juveniles penetrate the intestinal wall adjacent to the liver and then encyst in the peripheral tissues of the liver. Cannibalism among the fish seems to help the establishment of the encysted worms for normal development within the intestine. The life-cycle of the worm is neatly geared to the feeding habits of the host fish. A number of transport hosts have also been observed. Study has also been made on the morphology of various developmental stages of the worm.