204 
A. A. SANDOSHAM 
were present in the tissues of the body but no tetracotyles were seen. It was noticeable that 
the metacercariae in the snails that died earlier exhibited relatively greater motility within the 
cyst wall than did those found in the snails that died later. 
Feeding Experiments 
Six one-week old ducklings were brought from hatcheries and daily examination of faeces 
over 3 days were negative to eggs of helminthic parasites. Feeding of infective material was 
carried out as follows :- 
Duck A. Given, mixed with food, snail tissues containing approximately ioo 
metacercariae with 37 collar spines. 
Duck B. Similarly fed with snail tissue containing approximately 20 metacercariae 
with 43 collar spines. 
Duck C. Similarly fed with snail tissue containing a mixture of both types of 
echinostome metacercariae. 
Duck D. Similarly fed with snail tissue containing a few (about ten) tetracotyles. 
Ducks E and F were kept as controls. 
A white rat, bred in the laboratory, was fed with snail tissues containing approximately 
ten metacercariae with 43 collar spines. 
The faeces of ducks and rat were examined daily for eggs. Ducks A and C were seen to 
be smaller in size than the others at the end of two weeks. 
Duck A showed the presence of a few operculated trematode eggs (Fig. 6 a) eight days 
after the feeding. The eggs increased in numbers until it died as a result of an accident 26 
days after the infective feed. Post-mortem examination revealed no infection in the lungs or 
gall bladder but 21 adult echinostomes were present in the caecum and one in the small intestine. 
Duck C showed the presence of the same type of eggs as passed by Duck A commencing 
on the thirteenth day of the infective feed. On the twentieth day a few slightly larger and 
denser type of trematode eggs were also present. From the twenty-eighth day the number of 
eggs passed began to diminish and as spontaneous recovery was feared. Duck C was killed and 
examined for adults. Only one adult of the same type as obtained from Duck A was recovered 
from the caecum. 
Ducks B, D, E and F and the rat continued to remain negative for helminthic eggs in faeces. 
Development of Eggs (Fig. 6) 
The fresh eggs, which were examined under a coverglass so as to eliminate errors arising from fore- 
shortening, are oval and of uniform size measuring 0.1 by 0.057 mm. The eggs have a refractive smooth 
thin-wall shell with a yellowish tinge. The operculum is at one end but the slit is faint and difficult to see. 
At the opposite end the shell shows a slight thickening. In a freshly-laid egg the ovum is a single-celled 
and prominent globular body measuring about 0.017 mm i n diameter and is most often seen at the non- 
operculated end of the egg surrounded by masses of faintly brown granular balls. 
A number of eggs was transferred to some tap water in a petridish and kept in the 29°C incubator. 
Their development was watched day by day under the microscope by making temporary mounts as 
hanging-drop preparations. The division of the ovum is rapid and as it develops it seems to move towards 
the centre. The morula stage is reached in seven days and the development of the miracidium takes 
sixteen days. The developing miracidium is oval and centrally placed at first but gradually it lengthens 
until it is longer than the shell when the lower end of the miracidium bends over. It now occupies one 
side of the egg case, the rest being filled by two large globules of oil-like substance which get pushed about 
as the miracidium keeps stretching and moving inside the shell case. Under the oil-immersion lens two 
flame cells can be seen vibrating at about the middle of the body. Near the anterior end can be made out 
the developing pigment of the eyespots and a granular mass in front of it. The first batch of miracidia to 
hatch out had taken 24 days. 
The Miracidium 
The newly hatched-out miracidium is extremely active, swimming rapidly and incessantly by means 
of the cilia covering the whole of the body. The epidermal cells from which the cilia arise are arranged in 
four transverse rows of which the cells of the anterior row are the smallest. The miracidia in the living 
state measure 0.12 mm long and 0.042 mm at the broadest point near the anterior end. 
STUD. INST. MED. RES. 
