THE INTESTINAL PROTOZOA OF FROGS AND TOADS. 263 
refractive bodies (reserve material). ‘he cysts are spherical 
or somewhat ovoid and measure 18-22 4 in diameter. Occa- 
sionally—as in fig. 92—a clear area can be seen in the 
centre, in optical section, This is probably the nucleus, 
If such a cyst be kept under observation for some time it 
is seen gradually to undergo internal changes. ‘The contents 
slowly become divided up into five masses—at first irregular, 
but subsequently recognisable as four sporoblasts and an 
oocystic residuum (fig. 93). This process of segmentation is 
very slow, and takes from about twelve to twenty hours for 
completion. No nuclear changes were ever made out. 
The changes which now ensue concern the metamorphosis 
of the sporoblasts into spores. At first the sporoblasts are 
spherical, with a diameter of about 7:5 w (fig. 94). In course 
of time they become oval, however, measuring about 10 yw by 
7m. They then begin to show a clear area of protoplasm at 
one spot, quite free from the refractive bodies (fig. 95). The 
time taken to reach this stage is about another twenty hours 
or so after the spherical sporoblasts are clearly differentiated. 
Subsequently the sporoblasts slowly change into spores. 
They acquire a membrane, and later begin to have a “ pseudo- 
navicella”’-like appearance (fig. 96). Inside the developing 
spore the refractive bodies heap themselves into a spherical 
mass, which later represents the sporal residuum. This stage 
is reached after about another six to seven hours. 
From this stage onward development proceeds more slowly. 
The spore-membrane thickens, acquiring a very evident 
double contour, with a knob-like eminence at either end. 
The spores are now markedly “ pseudo-navicella ”-like in 
shape (fig. 97). Inside the spore the clear protoplasm is 
very sharply marked off from the residual mass, which now 
lies centrally. The clear protoplasm can be seen gradually 
to become divided in a longitudinal direction into two 
sporozoites, which lie with their ends curled over one another, 
téte-béche (fig, 97). With careful arrangement of the 
illumination it can be seen that each sporozoite has a nucleus 
situated towards the middle of its body (fig. 97). They lie 
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