42 



PARASITES OP MAN 



like Bilharzia, are furnished with a single appendage, may like- 

 wise be seen in the ova of different species of Dactylogyrus in- 

 festing the gills of the pike. In the more strongly pronounced 

 developments it is easy to perceive how admirably these out- 

 growths are adapted to the necessities of the different species of 

 parasite to which they are severally referable ; and, even in the 

 case of Bilharzia, the trifling amount of anchorage furnished 

 by a projecting point is not absolutely thrown away. The 

 resistance will also be greater where the spine is situated a little 

 on one side of the pole of the egg, which seems to need steady- 

 ing during the violent struggles of the embryo to escape from 

 its temporary abode. 



Fio. 10. Free ciliated embryo 

 of Bilharzia, with pear-shaped 

 rudimentary organs below the 

 head. Original. 



FIG. 11. Two ciliated embryos of Bilharzia; showing sar- 

 code spherules in their interior. That to the lett has 

 recently escaped the shell. Original. 



When any number of ova are removed from the urine and 

 examined, it will be found that a large proportion of them contain 

 embryos in an advanced stage of larval growth. The struc- 

 tural appearances presented by the embryos whilst still in the 

 eggs are remarkably uniform ; since, in all, the yolk appears to 

 have resolved itself into a mass of rounded sarcode-globules, one 

 or two of these particles being conspicuously larger than the rest 

 (fig. 12). At this stage, except towards the cephalic division of 

 the larva, no tendency to differentiation is perceptible; but 



