The development of the female Schistosoma mattheei was significantly higher than that of the
male (P<0,0001) in 12 sheep when each was exposed to equal numbers of male and female cercariae.
Many more male than female worms usually develop after infestation with pools of cercariae of mixed
sexes, a phenomenon which in the light of the present results seems to be due to a preponderance of
male cercariae and not to the more efficient development of male than female cercariae.
The female worms recovered fell into 2 distinct population groups as regards length and pigmentation.
Some overlap in the measurements of the breadths and in the numbers of ova in the uteri of the
worms, however, makes the demarcation of the different populations less distinct in these respects.
The female worms from 3 single-sex infestations contained either no ova (72 days after infestation)
or fewer (after 134-137 days of development) than the small females from the 12 sheep.
The number of large females (602) recovered from the mesentery was approximately the same as
that of the males (605) from this site. Similarly, although varying numbers of small female worms
were recovered from the liver of every sheep, only 2 males and 2 large females were recovered, and
these were from the same liver.
Because of the similarity between the numbers of male and large female worms, it is clear that,
for S. mattheei, physical contact with male worms is essential for development to maturity of female
worms, the mere presence of males in the host not being sufficient for this development to take
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