182 



ENTOZOA. 



embryos, capable of active progression wlien brought in contact 

 with dew on the blades of grass, rain-drops, pools of water, ponds, 

 and lakes. The prolonged action of moisture without, aided by 

 vigorous movements of the perfected embryo within, serves to 

 loosen the lid-hke end of the egg-shell, by the opening of which the 

 animalcule is set free. 



7. The cihated embryo, which is furnished with a solitary 

 X-shaped eye, after a longer or shorter period of activity, loses 

 its cihated covering, and becomes comparatively inert. It 

 alters its form, and probably soon afterwards gains access to the 

 body of a fresh-water mollusc, or, possibly, into the tissues of 

 a land-snail. 



8. Once within the viscera or substance of its so-called interme- 

 diate host, the Uon-ciliated larva probably becomes transformed into 

 a large sac, and developes new larvae within its interior. These 

 sac-hke larvae are called " nurses/' or " sporocysts," or, when 

 rather highly organized, "rediae." 



9. The contained nurse progeny or higher trematode larv^ are 

 probably furnished with tails, as in other flukes. When fully de- 

 veloped, they constitute the well-known Oercari^. 



10. The Cercari^ have a tendency to migrate from the bodies of 

 their molluscan hosts, and they are quite capable of an independent 

 existence. During these wanderings in the water, they are occa- 

 sionally brought in contact with the human body, and in a few 

 instances appear to have succeeded in penetrating the skin. 



11. It is not certain whether the Cercarise are taken into the 

 bodies of quadrupeds when the latter are drinking water or eating 

 sohd food, but it is probable that they are passively transferred in 

 either way. It is not unhkely that they are often swallowed while 

 still resident with the bodies of their molluscan hosts. 



12. From the digestive organs of sheep or cattle the Cercarise 

 make their way into the liver, in which new situation they proba- 

 bly part with their tails, and become encysted. This constitutes 

 the so-GaUed pupa stage. 



