1919] Cort: Eggs and Miracidia of Human Schistosomes 517 



the miracidium becomes active, often turning completely around. 

 Finally the egg bursts by s])litting, allowing the miracidium to escape. 

 The bursting of the shell seems to be due to the swelling caused by 

 the action of the water and not by any activity of the embryo. I 

 will quote Smith's description (1911, p. 64) of the hatching of the 

 egg of S. japonicum: 



The specimens shown [eggs of S. japo)iicum] are in the early unexpanded 

 state. At about 30° C, in the course of ten to twenty hours these eggs expand 

 to nearly or quite double their capacity and the miracidium, now in the 

 quiescent stage, moves actively about within the enclosure and with further 

 enlargement, the wall of the ovum splits and the embryo escapes, a free- 

 swimming ciliated organism. 



■exp 



Fig. 7. Diagrammatic representation of one side of the excretory system of 

 the miracidium of S. japonicum, from the lateral view; bt, bladder tubule; c, 

 capillary; exp, excretory pore; f, flame cell. 



The freed miracidium in the microphotograph (fig. 5) shows cer- 

 tain of the structural characters very clearly. The anterior region is 

 somewhat contracted. The non-ciliated anterior papilla shows very 

 clearly at the anterior tip. A short distance back from this, are visible 

 the depressions which mark the openings of the anterior ducts and 

 near the posterior end the openings of the excretory pores are also 

 marked by depressions. Some idea can also be gained of the character 



