510 University of California Publications in Zoology [Vol. 18 



it. The shell of the egg of S. mansoni is very tough and resistant. 

 Attempts were made to break open thp eggs and free the miracidia by 

 pressure on the cover glass. Often the egg would be pressed to twice 

 its normal diameter before the shell would break. Even then, in a 

 number of instances, the miracidium escaped undamaged. The inside 

 of the shell is lined with a thin vitelline membrane (fig. 4, vm). In 

 several instances when the shell was broken by pressure, the vitelline 

 membrane came away intact, surrounding the miracidium like a veil, 

 and it required considerable activity of the miracidium to free itself 

 from the membrane. Looss (1893, pp. 521, 522) described the vitelline 

 membrane in the egg of 8. haematobium as a colorless, finely granular 



Fig. 1. Micropliotograph of the egg of Schistosoma mansoni. Photograph 

 taken by Dr. J. P. Hickey. 



membrane with projecting nuclei here and there. The space between 

 the vitelline membrane and the embryo contains granules and oil 

 globules. These oil globules are secreted by the anterior ducts (fig. 2, 

 ad). Holcomb (1907, pp, 66, 67) speaks of these oil globules as 

 opalescent bodies and considers them to be food for the embryo. The 

 anterior ducts and their secretion will be discussed more fully in con- 

 nection with the description of the miracidium of 8. japonicum. 



When freed from the egg the miracidium swims actively, rotating 

 on its long axis. The shape assumed in swimming is similar to that 

 of the miracidium of 8. japo)ticum (fig. 5). The miracidium is very 

 mobile and changes its shape greatly when pushing through the 

 debris on a slide. I have seen no such extreme elongation as Holcomb 

 (1907, fig. 4) figured, and believe it very improbable that the mira- 

 cidium of *S'. mansoni could possibly assume such a shape while swim- 

 ming. The anterior papilla, which is the only part of the surface of 



