P. Manson-Baiir and N. H. Fairley 37 
being practically filled by a fully developed ciliated miracidium (Plate III, 
figs. 1 and 2). 
The following table, Table I, will serve to illustrate the main difference 
in the ova of the three species of Schistosoma. 
Table I. 
Differences in the Ova of the various Schistosomidae a ffecting wan. 
Schistosomum japonieum 
(Katsurada, 1904) 
vel. S. cattoi (Blanchard) 
(]) Ovum 70-75 pi long, 
45-55 fj, broad 
(2) Shape more rounded 
than other species 
(3) Spine. No spine but a 
rudimentary lateral 
papilla 
(4) Excreted in faeces, 
not in urine 
SchistoHomum mansoni 
(Sambon, 1907) 
Ovum closely resembles S. haematobium, 
but is on the average slightly shorter 
Shape Oval or spindle-shaped 
Spine. Lateral spine 
Excreted in faeces, less frequently in 
urine 
Sch istoHomum haematobium 
(Bilh. v. Sieb. 1852) 
Ovum 120-1 GO g long, 
40-60 u wide 
t 
Shape Oval or spindle- 
shaped 
Spine. Terminal spine 
Excreted in urine and 
faeces 
Hatching of the Ova. 
The ova may be readily hatched out by lowering the salt content of the 
fluid which bathes them, this occurs best at a temperature of 100° F. Micro¬ 
scopically, the first change noted under these conditions is a movement in the 
lateral walls of the ovum, at the point of its greatest transverse diameter. 
Activity of the cilia covering the miracidium is then noted and fluid currents 
appear to be set up within the shell membrane. This actual process, we believe, 
is due to the chitinous envelope and shell membrane acting conjointly as a 
semipermeable membrane, with the resultant passage of water from the fluid 
of lower to one of higher osmotic pressure. This ingress of water swells out 
the spindle-shaped ovum and increases its transverse diameter, and the mira¬ 
cidium, stimulated by the change in its environment, starts its ciliated activity. 
These two factors result in rupture of the chitinous shell in a lateral direction, 
as a general rule, slightly posterior to its central transverse axis. 
Occasionally free miracidia may be found in freshly voided urine or faeces, 
but such an occurrence is very exceptional. After rupture of the chitinous 
envelope the miracidium still enveloped in the shell membrane may be seen 
partially extruded through the opening thus produced. Rupture of the 
membrane generally occurs during this process of extrusion, and is probably 
due to its tearing on the jagged chitinous edges. Once freedom is attained 
the miracidium swims rapidly away on its adventurous quest. 
Miracidia. 
A limit of 36 hours is set down in which the miracidium must meet its 
specific intermediate host. In structure it closely resembles the miracidium 
of Fasciola hepatica, the most marked difference being the absence of eve spots. 
